[Split] Failing to upgrade from 3.2.8 to 3.3.7

[graficodestudio]

Hello,
I've been trying to update phpBB 3.2.8 to 3.3.7, following the exact steps from the official update procedure (keep on the server config.php, /ext, /images, /files, /store - delete evrything else - upload files from 3.3.7 zipfile minus the above files and folders), and I ended up with the same error OP posted (symfony's "FileLocatorFileNotFoundException").

I tried, and re-tried, and re-tried, always thinking I was missing some step... Without luck.

I'm posting this because the only way I was able to solve this was to do a fresh 3.3.7 install and then changing the database to the old one.

While this must sound completely unorthodox (and maybe even unbelievable), to my surprise I was able to get both FILES and DATABASE aligned with the latest version, 3.3.7, without errors. The only thing I lost was the graphical customization, which honestly was the least of my worries.

I know I'll probably get bashed here for this, nevertheless I'd like to ask: how is this possible? I mean, I would expected some sort of failure, maybe not the very same symphony error, but something similar... And yet, it worked. Also, now that I have this "frankenstein monster" installation, am I going to face compatibility issues of some sort (nothing actually happened up to now)?

Thanks in advance, sorry for my english, not a native speaker.