Similar situation to me in that applied for 820 (after PMV) in January 2018, received request for AFP report for my wife in March 2018 for the Sponsor "check"
I replied to the generic email address on the letter querying whether I could use an old AFP report from the PMV submission back in November 2016. They replied almost immediately and agreed to use the old report, completed their sponsor checking and stated the next correspondence I would receive would be from the Partner Assessment Team
I too got a little excited that things were starting to move but no further contact since mid-March
Anyone have any experience of how long the 820 processing time is after already being granted the PMV?