Some directory permission seem to change on their own

Alright! Would you say the change is something we the users will not even notice?

I have recently noticed the following effects, in fact I think they might be two distinct, not simultaneous, and possibly unrelated things: permissions on home changing to 711, and then home going unavailable:

[savchenk@login2 ~]$ ls -ld .
drwx--x--x 37 savchenk hpc_users 88 23 sept. 19:05 .
[savchenk@login2 ~]$ ls $PWD
ls: cannot access /home/users/s/savchenk: Communication error on send
[savchenk@login2 ~]$ 

Is the relation to the mentioned evolutions?

I just saw another user also experienced the second effect.