We have a deck that had Thomsons Water Seal Solid on it the past couple years. Horrible results. Peeling, mold in shady areas, etc. Our handyman is going to sand the flat surfaces and I'm inclined to re-stain with an oil based stain on the hope that it will penetrate and last. Any and all advice appreciated!
You will need to remove all. Once remoced you should be okay. Look at TWP Stains or Armstrong Clark:
https://www.deckstainhelp.com/twp-100-series-wood-and-deck-stain-review-2016/
https://www.deckstainhelp.com/tag/armstrong-clark-deck-stains/