В папке logs форума, есть такой файл your-vr.ru.error.log.
В нём такое:
[Mon Jun 05 11:28:26 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 11:30:11 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 11:32:50 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/?_fromLogin=1
[Mon Jun 05 11:40:57 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 11:43:46 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 13:08:48 2017] [error] [client 188.131.126.92] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 14:28:46 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:30:04 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:31:59 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:34:16 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:35:13 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:37:25 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:40:32 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:44:49 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:45:01 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:45:11 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/forum/43-aksessuary/?do=add
[Mon Jun 05 14:49:06 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:54:30 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:59:05 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:59:05 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:59:05 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 14:59:05 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:04:06 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:04:23 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:08:11 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:08:45 2017] [error] [client 94.243.81.42] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/424-cena-na-ochki-dopolnennoy-realnosti/
[Mon Jun 05 15:12:05 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:12:13 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:13:42 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:26:09 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/481-besprovodnoy-htc-vive/
[Mon Jun 05 15:27:52 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/452-5d-kinoteatr-ot-aet/?_fromLogout=1&_fromLogin=1
[Mon Jun 05 15:36:43 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 15:37:00 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/481-besprovodnoy-htc-vive/
[Mon Jun 05 15:51:26 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:03:30 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:03:49 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:04:30 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:04:49 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:05:14 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:05:39 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:07:10 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:10:15 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:11:15 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
[Mon Jun 05 16:16:33 2017] [error] [client 95.54.248.216] Premature end of script headers: index.php, referer: http://your-vr.ru/topic/482-dsfsdfsdfsd/
Решено переключением с php 7.1 на 7.0. Хотя раньше было на 7.1 всё нормально.