I have 4 plants, half my tent, on Mantis. Now in early bloom, 2 have slightly yellowish leaves from bottom to top. For these, I've started adding 1 g/gallon (1/5th my normal dose) MegaCrop and a small dose of micronutrient supplement (Earth Juice MicroBlast). But the 2 affected plants are the largest of the 4, and are larger and with more branches and buds than I usually get, so maybe they just need more nutes. I'm also supplementing with foliar feeding (using Transport) with high-N cal-mag (the AN version; I finally have a use for this with all of its N), Earth Juice MicroBlast and some kelp. I'm growing in hempy pots, using standard rectangular plastic office waste containers (≤4 gallons), with pure perlite at bottom (along with water) and the rest 80:20 coco/perlite. Plants are overall consuming more feed than other grows (using MegaCrop and AN pH Perfect before that). I use tap water, usually 225-240 ppm, with no pH checking or adjustment.
Overall, considering the work and time avoided, fully satisfied with Mantis so far. I often see some yellowing in late veg, early bloom, so nothing really new or different here (for me).