Can you see the manufacturers name? Are there model details anywhere, perhaps underneath? Personally, I don’t like the quality (lack of) of workmanship which leads me to believe that its not safe.
Yes you can use Varilite v-pro dimmer modules in a drilled blanking plate but keep in mind the holes shouldn’t be circular, they have 2 flat edges to stop the module rotating if retaining nut becomes loose. If you over tighten retaining nut it can hinder switch clicking in and out smoothly...
If the dimmer module retaining nut on the front of the plate is too tight, that can lead to a sticky switch. Though I cant see how this would tighten by itself.
I’ll suggest that it could be poor contacts between the lamp and the lamp holder. Poor contacts = overheating. You don’t have issues with the chandelier because it could be newer? Before you go poking fingers/screwdrivers/chisels/hammers into lampholder, I suggest switching off at consumer unit...