I tried Max2016+Corona 1.6.1 and a fresh Max2018+1.6.1, tried every option (local/UNC/other-than-C-drive). It just does not save out a single map. Rendering is ok even for multiple objects but obviously no save happens.
I´ve found a few old Mantis entries (and Romullus having the same issue once) but they do not really help. What do I miss? When switching to MR with the same setup everything works fine.
Thanks and
Good Luck