If timers are disappearing out of nowhere, and you’re running into strange disk space errors, you might consider contacting Athom to see if there’s a possibility that they can check if your hardware is malfunctioning.
There are more people encountering lost timers on 1.5.13 . I understood from Athom that losing settings ( a timer is basically a lost setting ) is a known issue on 1.5.13 ; it could be related to the diskspace issue: when updating timers, it rewrites settings to disk. This might fail when the diskspace is full. As far as I know, There is no feedback from Homey if writing a setting failed, so this can’t be checked.
Athom also suggested that this (‘losing settings’) is solved in 2.0.
As @Dijker suggestes: remove insights to clear up diskspace.