I have the zelzah which I have set to midi clock and remembered it being fiddly.

Just had a glance at the deco manual, looks like the midi sync setting is per preset, so dunno if you use presets and missed that detail when switching between, you would lose sync. Weird about the lag time knob behaviour, it looks like from left to right while synced to midi clock its lowest to highest division of the clock signal, which seems to be the same when not synced.