People always seem to forget about traffic analysis, and yet traffic analysis was a big deal in monitoring encrypted traffic even back during WWII.
https://www.theregister.co.uk/2018/08/10/internet_of_things_encryption_snooping/
Some countermeasures are very easy. For example, a device could be programmed to exchange a fixed amount of data on a predefined schedule. It can the batch whatever it cares about into those communications, and use random filler for the leftover space. Easy, yet seldom done...
