I have noticed with the Fujifilm GFX 50s II (and similar models) with the only contrast based AF [means Autofocus] that the AF accuracy isn't really that consistent. You can at times get OOF pictures - meaning that the focus lies in front of the desired spot. Instead of putting it for example at infinity, i get sometimes images that are front focused (closer to the photographer). I remember this also from the first OMD Olympus model, the EM5 from 2012, that this occasionally could happen.

Adapted lenses less consistent AF ?

It seems to happen slightly more often with adapted lenses on Fujifilm GFX 50 models, than I'd like. A stronger tendency with NON Fujifilm lenses compared to native Fujinon lenses. So, when you adapt Canon and Tamron AF lenses via the Finger Pro adapter for example (I don't think the adapter is to fault - it gives very good support). I think the sensor itself is a limitation as it only supports contrast based AF. Which always has been a twitchy architecture for AF.

Sometimes I feel that I fare safer with MANUAL focus compared to using AF (= AutoFocus)

The alternative when AF is enabled is, that I take several AF images instead of just one or two. Well, now that I know about this potential issue, I keep it in mind. Often checking that the focus is really went where wanted it to be.

A little bit sad.

On the other hand - well - let's call it a bug or a "feature". It is a medium format camera. Out of tradition, those type of cameras have always been a lot more demanding.

Requiring you not to "cheat", e.g. not to perform sloppy / too "fast" work. To double check things, such as AF in particularly. Especially with adapted lenses it seems even more vital to do so. Or simply go over to manual focus - because let's face it: A medium format camera isn't really meant to be emulate a fast working mirrorless fullframe camera.

Those are two different worlds.

What about the Fujifilm GFX 100 models ?

I don't know how things work with the newer Fujifilm GFX 100 models, due to that that sensor additionally supports PDAF, with pixels that were designed for better (and somewhat faster) focus. This helped Olympus a great deal once they implemented PDAF on top of the contrast based AF. I am assuming that the newer designed 100 MP sensors in the Fujifilm GFX are more sure in focus ?

But I lack any experience of that, because I don't have any GFX 100 model. (It is more the camera tech that i think is better - but comes with whose whopping 102 MP I really don't need - nor desire, to be honest).

100 MP is beyond overkill in many ways (I don't car how "cool" you think 102 MP is) One thing for sure is, that you need the latest computers as the dealing and post processing with those huge files, make the computer seriously strained. Not to mention huge space space on hardrives.

I think 50 MP is superbly enough. And frankly; I love the 20-30 MP range best (most of my cameras have 20 MP, one has 30 MP, another has 18 MP, and my Sony A7s with its hypersensitive, awesome sensor, has 12 MP). They are all more than plenty.

Nevertheless - there has never any medium format 50 MP sensor (33x44 mm) with PDAF embedded. Simply because the one used in the Fujifilm 50 models, Pentax 645, and first generation Hasselblad X1D, are from 2014 (And being damn good sensors, for being that "old"). But as i said... no PDAF.

I try to learn to deal with that the GFX 50 models have higher inconsistency / less consistent AF, especially with adapted lenses I need to be really careful. Usually, I work much slower with medium format cameras anyway, so manual focus isn't really the end of the world.

It often works better than it sounds, once you get used to it.

In the first two photos below

which I took with the adapted Tamron 45mm f 1.8 - with aperture ƒ8 - focussing onto the houses without any trees. One image was front focused. The others, I focused with manual focus in order to make that sharpness would where it should be.

Bummer... But it worked.

So, now I will keep an extra eye especially with ADAPTED lenses.

I remember this sometimes happened with the adapted Canon EF 300/4 L IS lens, when using AF. While the general AF has gotten better since the latest firmware update for the Fringer Pro adapter. Yet still - there is this inconsistency left, better checking twice.

That - i need to keep in mind.

I should add, that when I use AF, i use single focus AF, not continuous AF (where rhe camera re-focuses constantly). I've always been a single AF focus type of guy, albeit I changed my behaviour partially with the Canon EOS R6, where i sometimes use tracking AF / continuous AF (because it works very well, that's why).

I am not sure how (or if) the Fujifilm GFX 50s works with continuous AF, neither with native Fujinon lenses nor with adapted lenses. Perhaps I should test that...