Your slot quota:

[JumboShrimp]

I have not noticed this on the slot screen before:

Your slot quota:  35 new slots per 5 game days 

Is that 35 slot sets (of 7) or 35 individual slots?

Explanation says:

"This is the maximum number of slots you can acquire from this airport within this time period.

Slot quotas are temporary and are made to give everyone a fair chance to get the slots."

[dmoose42]

35 individual slots

[schro]

"Feature" announcement:
https://www.airwaysim.com/forum/index.php/topic,26356.msg296239.html#msg296239

One of the many bug reports that I opened about its botched implementation: https://www.airwaysim.com/forum/index.php/topic,54766.0.html

[JumboShrimp]

Interestingly, it was there (the message) and then it disappeared and I haven't seen it since. 

I did not notice anything out of ordinary about the airport (bankruptcy releasing a number of slots) or anything out of ordinary with my pace of taking slots (I either did not use up any or only very few slots).  So it is kind of a mystery.