The users of Google Tag Manager may have to re-verify their site ownership in Search Console, as advised by Google.
Recently an issue was found in the verification method of Tag Manager, which has been solved as said by Google. The reason behind this issue is unknown but due to it, many sites lost their verification in Search Console.
It is not been clarified by Google, however, they said the issue has been fixed and verified Sites may need to verify again in Search Console.
Recommendation: Colors On Google Search Console Reports Were Updated
We had an issue with the GTM verification method in Search Console, but it should be solved by now. You might need to re-verify. More details on how to verify at https://t.co/OkEwe4YvJv
— Google Webmasters (@googlewmc) February 3, 2020
How will you know if your site needs re-verification?
It is very easy to know if a site needs re-verification.
By logging into Google Search Console, if the owner finds the same previous data is still there, then there is no need for re-verification. If a site needs re-verification, then the owner will be asked to do so at the time of logging into Search Console. Other methods can also be used to re-verify the Site, however, Tag Manager is just one way to do so. There are many other ways too.
The video below will guide the way of re-verification or Google help guide can also be used.