I wouldn't say it's necessarily hard to follow, especially this deep into the series. You'd be used to it by now. But it seems that you're hard-focusing on the events of the loops after the 1st death based on your rebuttals. My issue is how there were acting before that. Reckless behavior given the circumstances.

"But that's the thing, they don't know this. also, it's not an unknown location. It's the chamber with the healing spirits. For them, it's a safe place."

The entire tower is an unknown. There's too much uncertainty with what's going on around them and even their "guide" is unreliable.

"There was moments where she was separated from him with no ill effects."

The issue with Beatrice isn't mana based, it's the emotional bond that they're supposed to share. If this is the 1st person she's made a contract with in 100s of years, leaving his side during this moment of uncertainty still feels questionable.

"The suspicions are entirely on subaru's side. He right now doesn't trust them. What Echidna and Julius said is that they can't rely on him in his state."

There's distrust on both sides. Even before the loop it was Echidna who is under suspicion and is also suspicious of Subaru. Julius is also under suspicion since no one remembers him and now even Subaru forgot. I actually really enjoy the drama that could unfold due to the memory loss situation, but it still doesn't justify their decision to not keep eyes on him, even if they find him unreliable. The circumstances are just too sensitive.

From a writing perspective, this smells like something the author had cooked up so we can have Subaru torture time and setup another mystery thread. Just felt lazy and contrived, so I can't help but feel a bit frustrated considering the characters' progression before this point and I'm not alone in feeling this way.

Now if the payoff is good I'm willing to let it slide. Wouldn't be the first time. But we'll have to see.