Ran into a weird situation in my lab where entering maintenance mode from the Web Client while attempting doing a full data evacuation WHILE there’s a failed disk in the disk group. It looked like it was unable to enter maintenance mode because one VM couldn’t get moved off the host, the reason? I’m not exactly sure.
Short very un-completely analyzed answer for me was either don’t do a full evacution, or vmotion the VMs to a different host BEFORE attempting to evacuate it. My situation was also weird because I had 1 out of the 2 magnetic disks in a failed state in the single disk group in the host that I was attempting to move away from.
I canceled the task after it ran for 12 hours, moved the powered off VM with a normal vmotion, then entered maintenance mode AOK. Sorry for the complete lack of detail, but nothing came up on teh interwebz for VSAN maintenance mode hanging at 65%.