Have you also noticed you're not encountering many or even any natural spawned master missions? Then read further! I have done ~180 Maven viewed maps and not seen a single master mission. For reference, here are what my masters and Atlas look like:
My current map device master missions. I've done 2-3 Daily Einhar missions on white maps, and banked every single other mission.
I began tracking all of my maps with a spreadsheet Tuesday night when I realized my Niko, Alva, Einhar, and Jun were all stuck at Act level progression. You can watch my tracking live on this spreadsheet. Every time I run a map I add an entry. Open it up and you can feel my pain in real time!
I have only seen two Zana missions, and they were both on NON-Maven maps. The first was before I had progressed the Maven questline in all regions (so Maven was not yet available). I hypothesized that the Maven being present might be the problem, so I ran a bunch of non-Maven low tier maps I was missing completion on Tuesday night and started tracking my completion about halfway through. Lo-and-behold - I got a master mission within 10 or so maps.
I have also taken screenshots of every single map I've run since I began tracking. Here's Day 1, and here's Day 2. Day 3 is a work in progress of course ;)
So, if you're mapping and feel like you're not seeing any masters.. you probably aren't. Try mapping without Maven and see if you get the same result as me. I'd love to hear if anyone else is getting this problem.
Some other notes:
Secondary league content is unaffected. I see plenty of Breach, Legion, Blight, Harvest, etc. etc.
For whatever reason, not everyone is affected by this bug. My wife and the other people in my playgroup are receiving natural master missions in Maven maps.
I have completed all of the master quests from the acts and invited them to my hideout.
There is a bonus Toucan in one of the albums
From RhysGGG: "Natural master mission chances were unchanged in 3.10.0 (still 10% for a random master, of which there are 5 possibilities, equally weighted)." The probability of not receiving a single 10% chance master mission in 180 maps is, to say the least, astronomically small.