今天忍不住不想再看WordPress天天抱怨要升级php，决定升tm的。从5.6升到7.2（因为lnmp 1.6官配支持7.2，1.7才是支持7.3，不敢冒险），然后WordPress无压力运行，nextcloud成功暴毙500.
面对这个老问题，这次好好查了论坛，终于找到了解决办法：
Had the same issue, was able to load nextcloud with php7.0, and it broke when switching to 7.1 and 7.2; it was an opcache issue.
I suggest you remove the lines relating to Redis and memcache from your config:
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"memcache.local": "\\OC\\Memcache\\Redis",
"memcache.distributed": "\\OC\\Memcache\\Redis",
"memcache.locking": "\\OC\\Memcache\\Redis",
就是把config/config.php里面的三行关于OPcache的配置删掉 （如果配置了redis也把redis的删掉）。删了之后果然成功运行起来了。