How to encounter a harvest boss (Tier4 seed)?

farmed about 2 months in 3.17 and now 1 month in 3.18, with all harvest atlas points, never seen a harvest boss from a tier4 seed. Did I miss something? is there anything special to do to encounter a tier4 seed?

How many maps you've done is more important than how long you've been doing it. T4's are exceptionally rare. Harvest has been in the core game for a year and a half, and I've never gotten a boss in all that time. I only run maybe 50ish maps per league period though.

I see others say it takes anywhere from hundreds to over a thousand, and that seems reasonably accurate.

Ever since our new league with Harvest Zana Mod, I've ran EVERY map with Harvest on it. I usually get 1-2 T4 bosses every few days.

The simple answer is you are not running enough maps fast enough. I only take the plots with Reforge / Lucky Reforge / Caster / Sacrifice Maps / Currency / Implicit and skip everything else.

I don't know how much the other plots are worth because it doesn't matter to me, but if you are in trade; then you could craft with them or just sell them if you need the chaos to sustain Harvest map mod.