I've been through some issues regarding Treat Wounds during play, it seems to be too unreliable for a good adventure flow, breaks immersion and discourages pressing on.
I'm GMing Plaguestone with 3 characters: Melee Ranger with an animal companion, Crossbow Ranger and a Thief Rogue. Whenever Treat Wounds was needed, we felt something was off.
At 1st level, the three of them are trained in Medicine, sporting 12, 14 and 16 Wisdom for a total of +4, +5 and +6 Medicine. The idea was so everyone could heal themselves since we had no Cleric or similar character. Considering that, we are looking at 50%, 55% and 60% of success/crit success on Treat Wounds for Trained DC 15.
In a small group of 3, and I believe this would apply similarly on a default 4-player party, at least 2 of them (the melees, and sometimes the companion) would require healing after an encounter, sometimes all 3 would. The Boar encounter was specially damaging since it has high speed in conjunction with an accurate and strong Boar Charge move, which downed the ranged Ranger with a single blow.
A Treat Wounds failure heals nothing and puts the character in a 1-hour lockout from another try. After 3 consecutive failures (~10%, not that improbable), the character with 0 HP has yet to be able to stand. They spent a lot of time drinking tea with Trin while being bandaged for 30 minutes total in a span of 2 hours for... absolutely no effect, I could see the disappointment in my players' eyes.
Moments after this, everyone declared they were taking Assurance(Medicine) and/or Medicine related skill feats as soon as possible so the game would run better, if not for the mechanical effect, for the feeling that when they stop to heal, they are guaranteed to heal at least something.
Since I had already read all the module, just imagining Hallod's Hideout with such unreliable healing made shiver a little. With that in mind, I made a ruling on the spot. From now on, every time you Treat Wounds you heal for "success chance times 9 (4~5), doubled for 1h (8~10)", which would be something close to the average healing for 2d8 over time and promised to do some deeper math considering critical failures and successes and try to find a solution for that.
So, I bring this to my fellow players and GMs, am I missing something? Is this how it works? Have you had any problems similar to this?