As well as the core updates, there were spam updates in March and December. If you found your site recovered around the time of the second spam update (which wasn't at the same time as the core) then it was probably relating to the spam updates. If so it's probably not HCU related.
We noticed something similar for a few sites. Including some that dropped to zero that spurred back to life and now have more traffic than they used to. Eg:
https://snipboard.io/lFmkpJ.jpg
Note the timing of the traffic uptick:
https://snipboard.io/N5XGAz.jpg - it aligns with the spam update, not the core.