[WPMU DEV Dashboard] css is not applied

hi there,
you informed me on 2020-06-05 my website ist down and later that it is online again.
If I Look at the site there it seems that is no css is applied at all!
I had a similar problem with a destroyed layout on another site. After deleting all WPMU DEV plugins it was ok.
I must mention that my site is currently in maintenance mode.
Thanks a lot in advance!