VM131, bad reaction on switch ON/OFF

I have a VM131 dimmer module.
It did work fine for several years.
Since a couple of weeks the dimmer has a bad reaction on the switch.
It seems it has lost its previous setting, when you press the switch the lights dont switch on, you have to press the switch for a long time before the lights turn on slowly again.
Can you help me out, is it possible that component needs to be replaced, can you supply me with a schematic drawing?
Thanks in advance, Jan.

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