First up I must admit to having been slack updating phpBB, it's been trouble free since it was installed 3 years ago so we are still running v3.1.6. While I should take the opportunity to update I think I'm going to need to fix this problem first anyway.
Cause: made a small text change to the header (something I did plenty of when first installing phpBB)
Issue: seems cache cannot rebuild
Error message: Fatal error: Class '__TwigTemplate_f1ad41c41d5dcebd1936e8a5fc939a2719b5029b90756be9aff410128a9695af' not found in /public_html/forum/vendor/twig/twig/lib/Twig/Environment.php on line 346
I have tried deleting the files in the cache folder which added an addition error regards file_put_contents() being disabled. I have spoken to my webhost and this function has been re-enabled, which has restored more files to the cache folder and left me with just the original error.
Given that editing the header has worked in the past, I am currently assuming there have been other security changes in my hosting which are at fault which may well cause issues with newer versions.
I do not know what other changes might have been made but I have a list of all disabled functions here:
Are any more of these required?
Apart from a theme, phpBB is stock with no extensions. Running php v5.6.38.
The admin area gives WSOD, no error log. We've probably not tried logging into that once the forum was set up.
If the best approach is to try upgrading first, please let me know. Open to all suggestions!