Yea definitely the indicator, today I actually had the opposite effect happen.
So I climbed and noticed it’s was bugging out again so I dove, and the indicator dropped even though I was screaming through the air, I checked tacview after and it showed a speed loss during the climb and speed gain during the dive as you would expect.
I just don’t know if maybe this is something the indicator would do in the real aircraft due to the pressure? Maybe you have to let it equalize after steep climbs and dives? Or maybe just a good ol fashion bug.