Most spells don’t require active concentration. In the event that you use invisibility sphere on ten people, you aren’t really continuing to concentrate on all of them actively as you do other things. The only act of real concentration is when you manifest the magic at the time of casting. Something like Black Blade of Disaster is the only real exception to this, as that spell requires the casters entire focus and if it’s lost - the spell ceases.
While you do have the option to remove self-contained spell effects, I’m not sure it would make sense to have that kind of option while unconscious, as your character shouldn’t be making any conscious decisions. I also don’t think it would make sense to lose all of the spells if you’re knocked down based on the fact that you can’t concentrate on them - aside from what I noted above, that kind of system would suggest that you need to make a concentration check any time you take damage or complete other actions, risking all of your spells to fail at any time.
Sometimes spells do fade when you are knocked unconscious. If you are KO’ed and the damage dealt brings your actual HP between -1 to -9, your spells remain. We have a script that functions to sometimes bring characters to unconscious state for attacks that would have normally killed them outright - if that instance occurs, the spells fade.
I do understand the frustration with trying to heal an invisible parry member - I’ve been in that situation before. I don’t think it’s necessarily a bug that you can’t heal an invisible character directly, however - as it isn’t possible to bind a wound you can’t see. There are quite a few options available though, including the characters having access to spells, potions, items, or scrolls.
Using see invisibility or true seeing will allow you to see and therefore heal any invisible creature. Using invisibility purge will dispel the character’s invisibility and bring them back into sight. Using a healing circle spell or scroll in the general area of an invisible creature will heal them - and there are two cleric feats that function in a similar AoE manner.
All in all - there are trade offs to a lot of spells and abilities on PoTM. Invisibility carries this small risk, so always be prepared!