One (okay, several) mistakes I've made in inspecting comb in a TBH:
I would lift the top bar, and forcefully drop the bar back on the hive to drop the bees off the comb so I could see it better. This works, but I have lost the comb too!! You'd think I'd learn after the first one.
The broken comb was usually with honey. I guess honey weighs more and the comb is more fragile (new, fresh comb).
Just an FYI for you....
You have to be very careful with topbar hive combs, there is no side or bottom supports and its soft new comb and its usually very heavy.
As you now know, never bang it, but also if you have to turn it make sure you turn it slowly up and over, never tilt the comb straight out away from you or it will snap off from the weight of it.
Yea never do anything violent like shake or bump the comb. Just gonna upset the bees. You can typically just leave them on the comb for inspection. A gentle blow through your veil will cause them to move if you need to look at a certain area. Or if you use smoke a few very small puffs would get them to move as well.