I have an update on my earlier reply.
I indicated that, I my case, the issue with the Credential Manager was related to MSI Dragon Center.
However I recently learned that there is a deeper cause.
I was using MSI Dragon Center only to control LED lights on my GPU. On every Windows logon Dragon Center applied LED settings. I then ran a scheduled task via Windows' Task
Scheduler to stop all Dragon Center services/programs. It appears that the issue may not be related to Dragon Center itself, but to the related task in Task Scheduler.
I noticed that whenever I create a task in Task Scheduler using my local Windows account and choose the option 'Do not store password. The task will only have access to local computer resources.', the Credential
Manager starts forgetting my stored credentials. The task itself runs fine, by the way.
If I opt to save my password in Task Scheduler, then Credential Manager remembers my stored passwords.
Not sure whether this helps, but if you are using your own scheduled tasks, this might be worth checking.