There seams to be an issue with the 4090 2X battery, part number BTRY-WT40IAB0H.

The newer Rev C version does not always lock into the 4090 and click into place, the previous Rev B version was very reliable.

has there been a design/production change or could this just be a quality issue?

Has anyone else seen this problem?  

Currently I have 10 back from a customer, it is intermittent (you can get it to lock if you slam the battery home), but easily re-creatable.