I have also noticed this issue, however, the only times I have had the 'sticking' occur is when I have had my LED batton lights turned on for a period of time (running at around 150W). Previously, to get around this issue, I swapped the Shelly 1L out for a spare that I had. When I tested the unit I removed, it worked perfectly. However, the replacement unit has just now displayed the same error. The switch state changes, but the light itself does not turn off; it remains on.
I don't feel like this is due to a high inrush current. Knocking it seemed to fix it, so maybe it's also to do with how hot the relay gets over time?