Errors trying to upgrade PHP

[GS]

I should be running G3 v3.1.5, which shows as "build 434" on the admin dashboard, or as v58 on the module upgrade page. I upgraded some time ago, but it's not impossible I'm missing an updated file or it didn't fully update - if that's even possible. It's also possible I don't have all latest modules since they moved to being updated on Github.

I've been running backported PHP 7.0 on Ubuntu 18.04 LTS, but am finally getting around to upgrading the OS and PHP versions. I tried enabling PHP 7.2 (a2enmod) and disabling PHP 7.0, which results in error output on most themes. Disabling all modules resulted in the same. Only a few themes seem to work, including 3nids, browny and Gallery Wind. I've been using the Wide Wind Click 4 Next for years, but this one is also affected. Oddly the Wide Wind theme seems fine.

Example errors attached as screenshots.

Any pointers on where to start would be appreciated.

[GS]

Well, that might have been easier than I thought. On a hunch I realized short_open_tag was on for php7.0 but off on 7.2's .ini. Changing both to on seems to have sorted this issue from what I see.

If I upgrade versions further, my understanding is PHP will still support short_open_tag even on the latest v8.x versions - are there any considerations to be aware of?