I've never heard of anyone having that sort of issue.
I regularly fly with 6 batteries and have never been asked about them.
In any case, the capacity of DJI batteries in watt hours is clearly marked on each one to help avoid any confusion.
I had this same issue I just updated the drone and it went away but all photoage I thought I had captured wasn't there because it was still telling me it was recording but when I stopped recording and went to check the video it wasn't there and...
yeah I just found that out I personally would still keep to just 2 spares just in case there's a confusion or some unforeseen conflict and also I don't want to have to carry anymore than that I'll find someway to misplace one of them if I have...
this doesn't include the battery already in the drone although I did just look the mavic 2 does fall under the 100 Wh exception as well as many other drones. although I'm surprised he wasn't stopped 21 batteries is a lot.