In this particular case, sweep expires sometime after you perform the reset. No, it does not expire on server reset, it expires like 1-2 hour after your survival reset. I'm not entirely sure why.

I will say this again.

After resetting survival, if you don't finish sweeping within 1-2 hours, your sweep privilege will be reset.

I suspect the game simply have no way of storing how much you are allowed to sweep for your "current run", instead it keeps track of how many you did sweep "previously" and that's what it uses to determine if you are allowed to sweep more. And a few hours after your reset, this "previous" value gets overwritten by what you have done on your "current run", which, as it turns out, is 0 due to you not using them. And as it calculates how many you should be sweeping for the "current" based on the "previous", you end up with pretty much nothing.

And your subsequent days will be based on their previous ones, which means you are rebuilding the numbers for scratch, which results in the pattern you see-you get a few more than what is previous allowed every day if you can complete the full trials.