Hi Everyone, I wish I can show you a picture but the page does not allow it until I reach 10 posts. The shop is about 45 minutes drive from here and this is why I been hesitant of taking the bike back there. The gearing is shimano 2 x 9, the bike uses a kmz chain with a missing link, I already bought a replacement chain just in case. What I am trying to describe is basically a smash mark in the chain like if one of the teeth of the crank or the cassette smash it hard on it, I get those every time I go for a long ride (20 miles). The way I been fixing it is by taking out the link and sanding a bit the part where its been smashed then assembly it back. If I don't "fix" it the chain link will get stuck and the chain will start skipping, I keep the chain well lubed so the issue is not lubrication that causes the stick links, the issue are smashed marks in between the links.
My last resort would be taking it back to the shop, so I figure I could ask here to see if anyone experienced something similar.