They used 2 different products, that does not sound right , stain does
not peel unless there was a reaction and the topcoat did not penetrate.
Ive never heard of stain peeling, paint yes. Best is remove it all ,
probably with a power washer. You should find out what products they
used and talk to the manufacturer. Warranty or no if they didn`t follow
instructions it is their fault. If it won`t power wash off with out
damaging the wood you will need stripper. Talk to who made the products
for advise.