The "RNG" in this games loot systems (drops / vendors) seems to be broken, or not random at all. I've spent the past couple days using the time skip method to refresh the gear vendors to "farm" for Epics. I was doing this on my Technomancer, and I saw a couple issues. The weapon vendor would only have certain weapon types as a Special deal, the normal list of guns would have all type. The Special deals would only ever show Snipers (both types), Rifles, Shotguns and Auto Shotguns... and nothing else, ever. I went from 3/10 til 4/16, each hour of the say AM/PM, and never saw any other type of weapon.
Next was that there is a pattern to having Epics spawn. The first one I saw was on 3/11 @ 5pm, the next was 3/12 @ 8am, then nothing til 3/22 @ 10pm followed by 3/23 @11am. When I saw that I skipped forward 11 days to 4/2, an Epic popped on 4/3 @ 3pm, then 4/4 @ 4am. Skipped forward to 4/14 and another Epic popped at 4/15 @ 9pm, then 4/16 @10am. This is something you would never likely to notice by just playing, but it appears that for my Technomancer, it is scheduled to have Epics on the vendors every 11 days-ish, one in the AM and then another in the PM. Very odd.
Some streamers have said they've seen the same patterns with their vendors (different spreads, but still a pattern) and also with Legendary drops (days, time frames and types).