After a lot of tries, first through zigbee2mqtt over a slzb06 coordinator… did not pair/ connect: it left the network because …
Then through ZHA over a sonoff coordinator it got connected. The correct device was recognised and the correct entities are available.
So i made 2 simple automations to switch on/off a lamp.
But when i push the buttons, nothing happens 
That generation of IKEA buttons are unfortunately just plain unreliable in my experience. I’ve thrown away several of them after they just stopped working, began draining batteries quickly, or other weird behavior. It’s a shame because they are small and can be fitted over standard wall switches without looking too terrible, but overall you are better off upgrading to the newer Rodret/Somrig/Styrbar models.
haha i was already a bit afraid that would be the conclusion.
I have some nice aqara opple switches that match the “normal” lightswitches - I used the IKEA as random to stick to my nightstand or on the table to activate scenes.
think i’ll bin them then - i never heard of the three models you mention but have not been at IKEA for a while…
