Tried various regex syntax, but cannot get it to match correctly.
I've based the syntax on official regex documentation, as well as tested the various syntax on online test-tools, and by all accounts it should find the journal entries.

Example 1:
Reconciliation label: 12345
Journal entry label: 012345

Regex: ^.([0-9]{5})

Here, regex doesn't find a match, despite " . " should stand for any character, be it number or letter. I've tried replacing it with \d, among many other variations, but to no avail.

Example 2:

Reconciliation label: a12345
Journal entry label: 12345

Regex: ^.([0-9]{5})

Here it finds the match just fine.
So it appears that, for some reason, Odoo doesn't interpret standard Regex rules as you'd expect(?).

Also tried it with https://regex101.com/r/4gbB6f/1 to avoid any dual matchings, but again, no dice.

Anyone know how to get it to match correctly using Regex in this case?

Already contacted Odoo Support, but after 1 week, I figured I'd best give the forum a try as well. :)