I finally got around to playing around with the ESP8266 breakout boards (ESP8266-01) I had sitting on the bench. The community support for these has improved a lot recently although there is still some signal to noise problems between old and new information when googling.
A little while ago an Android project I’m working was seeing infrequent but regular ConcurrentModificationError crashes and we were at a loss to reproduce and fix the issue.
It turns out that we were making a common but subtle mistake using SharedPreference.getStringSet(). We were operating on the returned Set object: in our case we would be filtering this Set before saving it again.