Lots of strange php and nginx related problems after upgrade

[MikaelLarsson]

Yesterday after upgrading arch on my raspberry pi 3 server I started to have some wierd issues with nginx and php. The most crittical issue is that some php functions in scripts that has been running perfectly for years now suddenly complains that the file system is read only.
...
imagepng() --> failed to open stream: Read-only file system in /var/.....
chmod() --> Read-only file system in /usr/share/webapps.......
...
My first thought was that the directory owner and/or permissions were screwed up after the upgrade, but they seem to be ok and I can create and modify files using the http user in a terminal.
...
[root@raspberrypi01 ~]# sudo -u http test -w <path to dir> && { echo YES; } || { echo NO; }
YES
[root@raspberrypi01 ~]#
...

I can't seem to figure out what's blocking php from writing files. If anyone has any suggestion of what could be wrong or something to test or look for please reply to this post.

[MikaelLarsson]

I'm answering my own post here to get it documented that I just partially got some of my problems resolved temporarily.
I got rid of the "File system read only" message by removing all symlinks from the different server instances root dir to every webapp running on that instance and then copied all the webapp files to every nagix instance root dir. Unfortunately, this means that files uploaded by a user in one instance will not be visible on other nagix instances running the same web app.