As Sumikito says, these threads are full of a black gunge apparently unique to rep factories. Its a mix of filthy cutting fluid, dirt, fine swarf and more dirt, and works beautifully as a glue and gap-filler!
You need to take the bracelet off the watch and leave it soaking overnight in acetone, nail varnish remover will do if it is acetone based. I use an ultrasonic cleaner full of acetone and strip the bracelet down into component parts to ensure every bit of it is cleaned.
Once it is clean, you'll find all the screws will tighten and untighten much more smoothly and the ones which used to stand proud at the head end might even now go flush.
Rebuild the bracelet with Loctite 222 on all the screws and oil the links with your chosen lubricant.
This might sound like a fair bit of work to remove a link from a bracelet, however, the watch will wear much better, you won't have to worry about losing screws and the thing falling apart, plus it'll get rid of the mysterious black gunge you'll now be able to see in ever crevice of your bracelet!