"receive 10k items from your clan" achievement progress reversing?

[oleler]

i've been helping a clan member reach said achievement, and while the progress has been slow, it has been steady. however i've noticed the progress i see in their achievement page is reversing.

for example, 2 days ago i sent them 120 medals from clan inventory, bringing the total to around 8200 items received. i checked their achievement just now and see it has gone back to 7900. what on earth is going on? is this achievement broken? i don't remember anything like this happening to me when i was working on that achievement

edit: wanted to add, i think this has also happened like a week or so ago. i had vague memories i got their count over 8k that day and the next day it was just below that, somewhere in 7k. but i wasn't sure so i just brushed it off. now though i know for a fact the count was at 8.2k items received.
unsure if this is a server sync issue and it just shows up to me incorrectly, but i do feel like the count was off even at 8.2k...

 

[oleler]

update: the count has not changed from ~7900 items received and i sent them another full stack of medals and the count jumped to little over 8000. the previous count of 8200 was not recovered and the true count i imagine would be 8500 by now. so it is starting to not feel like a server sync issue.

 

[oleler]

update 2: their progress has yet again reverted to below 8k. could devs look into this?