What a mess. Contact the credit union directly and ask them to fix it. If you can provide them with a copy/screenshot of last month's reporting and this month's, showing the account number change on a single tradeline as opposed to two separate tradelines, that'd be helpful in explaining what's happening.
I'd say just wait it out. Sounds like a Credit Karma alert and not really an issue on your proper credit report. Run it from annualcreditreport.com and see what they each show.
as of 1/1/23
