Hello and welcome to the forums!

I had such "slippage" symptoms happen to me for several years before finally figuring out what the actual problem was.
I guess you can say it intensified when it rained. In my case (and i suspect in your case as well) usually the largest chainring
on the CRANK - has significant wear to it - (the teeth are heavily worn down) and will not pull your chain properly anymore.

They will infact skip a beat so to speak..

You would be excused for not thinking the chain is able to skip a cogwheel of such considerable size and while the chain is committed
to such a big size wheelcog (50T in my case) So i naturally assumed it was the rear (smallest) cogs that was the problem because
the chain is in contact with cogs of such a small size. Well how wrong i was. Pretty distressing to look down and seeing it happen
and not have any idea where the problem lies. This was a real eyeopener to me as in all my years of cycling never thought this
could be possible and that cogs/chaindiscs did not wear, only the chain, lol. Maybe there is a significant difference between 26
& 28 inch bicycles. The 28" roadbikes always try for the lightest of alloys and i suspect these wear more easily than heavier
and more durable 26" parts where weight is not of the essence.


Try to find a picture of your chaindisc online and compare the teeth/tooth with the one you`re riding now. Maybe you`ll have
yourself an ephiphany. My two cents have been tossed.