We have a number of AudioMoth 1.2.0 with firmware version 1.8.0 or 1.8.1. and we use them to record bats.
Until recently they worked fine, but gradually they started producing thousands of nonsense tiny files (39-61 kb) and only a handful of good ones scattered here and there, even in areas with many bats. In some cases they produce only the tiny ones, and no big/good files at all. The settings are the same as before (see end of message for an example).
Yesterday I tried one device with settings in the audible range and it worked well (on my desk). Then I used the usual settings for ultrasounds and put it outside overnight - today I found out that the problem was still there.
We are trying with new alkaline batteries like Energizer and sd cards suggested by Open Acoustics