For a long long time the tooltip containing the number of items received / raids attended / ... stopped working for me, which is absolutely horrible for using this addon.

Edit: Removed the suggested solution since that was wrong.

Yesterday during our raid it suddenly worked for me, but completely broke as described for a different player on our loot council. Today is another raid, I'll report how it behaved there later.

For me today it's broken again.

Sounds a lot like you just closed the frame with the little ">" button to the top right of the voting frame.

I never pressed that button, but yea that is true. Still the tooltips are almost always broken and the suggested change does not help with that either:

Edit: I found one example that was a little less broken.

Interesting - never seen that before. I would like to have a look at your saved variables

When debugging earlier in a 2-person-raid everything worked just fine, but once I was in a proper 25-player raid it looked like that. Here's my saved variables:
RCLootCouncil_Classic.zip