I don't know if it's just me, but I find that, most of the time, I have to assemble Alps and Alps clone switches twice. That is, after reassembling the switch, I have to disassemble and reassemble a second time. Something just never goes back in the first time and the switch can't be fully depressed. Probably something to do with the return spring.
You may find that you can open the switch and reassemble it in case something isn't quite seated right. Simplified ("Fuhua"/"Fukka") Alps switches are fairly easy to open in place, but I've never tried it on a Matias switch — they do seem to have tighter tolerances on the support grooves for the contacts, i.e. a tighter fit, and it's the really tight fit of the contact plates in typical clones that makes them so freakishly hard to open and reassemble without first desoldering them.
I did notice that Matias quiet click switches do make a sound if they're not struck centrally.
The switches are of course transparent; I don't know whether you would be able to make out whether anything is wrong simply from a visual inspection.