I noticed that the argument I had in mind didn’t work out quite as intended in the previous Maxi Loop, here’s an updated version.

Rules Draw a single closed loop that connects cell centres horizontally and vertically, visiting every cell. Clues indicate the length of the longest loop segment in that room.

Here’s a Maxi Loop puzzle. It probably doesn’t quite deserve to be called “hard” due to the small size, but the intended logic should qualify.

EDIT: This didn’t quite work out intended, see Puzzle 91b instead.

Rules Draw a single closed loop that connects cell centres horizontally and vertically, visiting every cell. Clues indicate the length of the longest loop segment in that room.