Quark-r2.4-321.jar doesn't seem to be ignoring certain blocks when replacing for a biome. Blocks like Water, Lava, Stone Bricks, Wood Logs/Planks, etc. I haven't seen it override a portal frame yet, but if it suspect it's still possible that could happen from what I've seen. It also creates a lot of odd looking artifacts when mixed with liquids, sometimes water and lava get mixed due to the generation (slime biomes).

https://i.imgur.com/3ePzEYM.png
https://i.imgur.com/jcs4eZr.png
https://i.imgur.com/vRvMada.png
https://i.imgur.com/UvXaGyL.png
https://i.imgur.com/hKPMSC3.png
https://i.imgur.com/VuONohv.png
https://i.imgur.com/KwFww1J.png
https://i.imgur.com/GVgv8Zb.png
https://i.imgur.com/Dz1iu8q.png

Hello! Quark's moved to 1.18 now-- unfortunately, this means that (unless your bug is critical and/or game-breaking), we're closing support for issues filed for versions prior to it (e.g. Quark on 1.16).

If your issue still occurs on 1.18, or if your issue happens to be rather critical (e.g. consistently crashing the game with no other mods present), please leave another note or open a new issue. Thanks for your cooperation!