This was a problem in an earlier version of Trados Studio that was corrected at some point. Now it's back. Example:

Description: ERR: 3.4b: Remove comma separator if not included in German

RegEx source: (\b[0-9]{4,9}\b)

RegEx target: $1

Condition: Grouped search expression - report if source matches but not target

Source unit: August 2020

Target unit: August 2020

A warning is thrown during verification despite the target matching the source exactly, as required. The idea here is not to translate 2020 as 2,020. This wasn't hitting in Trados Studio 2019 SR2 (most recent version), but it hit on my very first project after upgrading to Trados Studio 2021. That of course reminded me of a year or so ago when this was a problem and then fixed in 2019 I believe.