phpBB Debug warnings, messed-up layout, on viewtopic.php

[kingjon3377]

When trying to view any thread, the page first fills up with log-spew type text, which is (too quickly for me to read it) replaced by a version of HW with a few lines of PHP warnings (visible) at the top, then the usual background image, and the HW header at the bottom of the screen, and (when I scroll down) the thread below that. A too-large font is used for most everything in the thread---essentially everything except the "Logout", "0 new messages", "View unanswered posts," etc., and the footer---and some posts don't show any text at all. The visible warning/log lines say:

[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 488: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead

(I first ran into this when opening an early-July topic-reply-notification email, but reproduced it on this thread linked from the "Announcements and Information" room directly.)

Here's a screenshot showing the log-spew and the dropped header:

And here's a screenshot after I scrolled down enough to show some of the messed-up layout:

[BarelyAPrincess]

Was caused by a PHP upgrade from 5.6 to 7.2. Temporarily fixed by muting PHP warnings but truly can only be fixed by upgrading phpBB.