Looks like hashrate is back up.
there is no evidence the hashrate ever fell
it cannot go "back up" if it did not even fall
Maybe I'm missing something, but it looks to me like there were only 114 blocks mined on 9/23.
596163 to 596276
https://www.blockchain.com/btc/blocks/1569268006726100EH/s at 11.8T diff should produce 170 blocks/day on average. If the nethash was actually at 100EH/s, the probability of getting <= 114 blocks is .00000319. Pretty unlikely.
90EH/s at 11.8T diff would average 153 blocks/day. Probability of <= 114 blocks is 0.000587, which is getting into the range of possibility, but still a once in a 5 year kind of event.
Calculated these numbers with this poisson distribution calculator :
https://keisan.casio.com/exec/system/1180573180Probability of getting <= X number of blocks in a day at 100EH/sec:
X | probability
--------------------
110 | 5.736E-7
120 | 3.248E-5
130 | 8.260E-4
140 | 0.01017
150 | 0.06519
160 | 0.2349
170 | 0.5204
180 | 0.7910
190 | 0.9400
200 | 0.9889
Probability of getting <= X number of blocks in a day at 90EH/sec:
X | probability
--------------------
110 | 1.574E-4
120 | 0.0033
130 | 0.0320
140 | 0.1560
150 | 0.4250
160 | 0.7307
170 | 0.9196
180 | 0.9852
190 | 0.9983
200 | 0.9999
edit: corrected to <= 114 blocks