Welcome back!
IIRC, the owner of MobileRead decided to go with a more worldwide-compatible Life+70 public domain rule, so all the stuff that was only PD due to Canadian Life+50 rules or the US pre-1923/copyright-not-renewed rules was removed from public accessibility and will not be available again until they are eligible under the new uploading guidelines.
There's a
post here in the Announcements forum about this and other changes.
Hope this helps.