This sounds very similar to a situation I am facing.

I had a tune up a month or two back. He commented of difficulty with my FD adjustment.

He put on a SRAM 9 speed chain and said he could not find slipping in the cassette.

I put on a new cassette a few hundred km later (I noticed slipping immediately after the tune up).

My issue is now this:

I almost exclusively ride in in the big ring. Since the tune up I have had consistent problems with my chain dropping to the middle ring, and then I have issues getting the chain back to the big ring. This did not change with cassette replacement.

I plan to do a complete adjustment on the FD this weekend to get it tuned, in case he messed up. I hope this solves it.

But I worry it may not since I never had it happen before.

Could it be:

Chain incompatibility? I have never used SRAM chains (honestly cannot recall my previous chain).

Worn big ring? I will check for shark fining.

Bike details

I am also on my third chain and second cassette.

The freehub body was new last year (so several thousand km).

The bike has about 10,000 km. It have Tiagra STI shifters, Tiagra FD, XT RD, low end Deore cassette (11-32), Andel crank (175mm) and I cannot recall brand of chain ring (26t-36t-48t(maybe 46t)). I have never had a problem shifting FD between big and mid rings, though some issues getting into small ring previously. I never used it so was not worried.