The Valhesia 3-3.1.9 modpack updated and gave updates to several mods including Quark.

I bought the issue up to people who help or work with the Valhesia Modpack and they directed me to report the issue to quark.

Blocks can be see through when interacting with vertical slabs from the mod 'Atmospheric'
According the people I spoke with in the Valhelsia discord this an issue with Quark.

Just FYI - I'm one of the Valhelsia developers, and I'm not sure if it's a Quark issue or not yet (I was asleep at the time this was reported). I think it was one of our volunteer helpers that may have directed you here. I can't reproduce it with Quark alone, which is why I didn't make a report myself, since I wanted to know which combination of mods were the minimum to reproduce the issue before reporting it anywhere.

I do know that both Quark and Abnormals Vertical Slabs have the same problem, and only in certain directions (from memory, North and West aligned vertical slabs have the problem but South and East aligned don't). I did notice that the code for vertical slabs changed recently, but I haven't had a chance to actually look at what the changes did.

I did rule out OptiFine completely. I've also noticed a similar issue with snow layers in certain configurations (edit: The Snow Layers were caused by the FerriteCore mod, not sure if that impacts anything else, haven't had a chance to test it), which leads me to think that it might be a different mod entirely doing some really bad culling, but I haven't the slightest idea as to which yet.

I can confirm this issue as well. It appeared after updating quark to 306 (befor that I had 304).
I just now updated to 307 and this issue is gone.

I can confirm this issue as well. It appeared after updating quark to 306 (befor that I had 304).
I just now updated to 307 and this issue is gone.

Did you update any other mods at the same time? Just updating Quark to 307 has not fixed it for me (nor can I see any code changes that would fix it between 306 and 307).

Edit: It looks like the entire issue might have just been caused by FerriteCore. Safe to leave it closed. :)

I can confirm this issue as well. It appeared after updating quark to 306 (befor that I had 304).
I just now updated to 307 and this issue is gone.

Did you update any other mods at the same time? Just updating Quark to 307 has not fixed it for me (nor can I see any code changes that would fix it between 306 and 307).

Edit: It looks like the entire issue might have just been caused by FerriteCore. Safe to leave it closed. :)

In fact I did:
collective-1.16.5-1.67 to collective-1.16.5-1.68
ferritecore-2.0-forge to ferritecore-2.0.2-forge

I did not think of other mods could be an issue as well.

@sarim No, because FerriteCore fixed the issue already in a recent update. I just only had a chance to verify that this issue stemmed from the same root cause a few hours ago, since the FerriteCore changelog only mentioned snow layer rendering.

Thanks, upgrading to ferritecore-2.0.2-forge in Valhelsia 3.1.9 (both server and client) solved the problem. Maybe time for 3.1.9a?

@Vaelzan is there an open issue about this in ferritecore?

@sarim No, because FerriteCore fixed the issue already in a recent update. I just only had a chance to verify that this issue stemmed from the same root cause a few hours ago, since the FerriteCore changelog only mentioned snow layer rendering.