Same problem. I had a client DA drop from 40 in January to 29 in Feb. Holy cow!
Looks like Moz did not recognize backlinks with 301 redirects that were previously recognized. Any thoughts on why these redirects were not included in the latest index? And - will this be reversed with the next index?
(redirects, in this case, were due to a new domain that was in place in mid-2017 - backlinks from the old domain had been included until this month).