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Issue description:

Nether Portal turn into "Missing Texture" Purple and Black, and when pass the portal, the portal is extinguished.
This bug only accured when Mekanism activied. If not install Mekanism, won't has this bug.

Steps to reproduce:

1.Use obsidian to make a portal, and ignite it.

2.Passed this Portal and get into the nether, the portal is extinguished.

3. Ignite it again.
   

4.Back to the overworld, the portal is extinguished again.

5.Ignite the portal again, and get in, it generated another obsidian door, next the first door.

Version (make sure you are on the latest version before reporting):

Forge: 14.23.5.2847
Mekanism: Mekanism-1.12.2-9.8.2.389
Other relevant version:

If a (crash)log is relevant for this issue, link it here: (It's almost always relevant)

No crash report
[gist/pastebin/etc link here]

Please post your complete mod list

I believe this was probably some weird mod interaction, but I am going ahead and closing this as in 1.15 we now use a forge hook for adding refined obsidian blocks as valid nether portal frames, rather than using a registry replacement, which should be a lot more cross mod compatible.

I am having this exact issue and it seem It's from Mekanism and LiteLoader being together.. causing the missing nether portal texture

Will there be a fix for 1.12.2 or it's unsupported for that version?

It is unlikely that 1.12 will receive an update as we are focusing on 1.15. Additionally, as forge no longer supports 1.12, even if we wanted to we would not be able to include the same hook in forge to not require doing a registry replacement.

Is there any workaround other than "remove LiteLoader"?

This is a pretty catastrophic bug for 1.12.2 Mekanism, but for anyone willing to do some technical digging and fix it for themselves:

using this branch, https://github.com/mekanism/Mekanism/tree/1.12

and commenting out registry.register(BlockBasic.BlockPortalOverride.instance); in main->java->mekanism->common->MekanismBlocks.java @ line 89 and then recompiling the mod and using that seems to fix most of the problems. I also commented out the overridden neighborChanged method of the BlockBasic class but I'm not 100% certain if that's necessary (this may even be bad to do, i didnt go looking around to see what this overridden neighborChanged method does elsewhere in Mekanism), I think mostly the registered BlockPortalOverride is what causes most of the problems.

This removes the ability to use the Refined Obsidian block as a component for making Nether Portals but in my opinion that's an acceptable trade-off to fix nether portals for Mekanism in 1.12.2. 1.12.2 is still a pretty widely-supported version of Modded Minecraft and some mods that I'm pretty fond of also became discontinued @ ~1.12.2 (such as Tough As Nails), it would be a shame for the latest supported 1.12.2 version of Mekanism to just not be apart of 1.12.2 modpacks because of this bug. I get that supporting multiple different versions of Minecraft, especially ones that are officially unsupported by Forge, is a big pain in the ass so hopefully this can help some people help themselves without having to bother Mekanism devs to patch this.

Apologies for lateness, but if anyone else is having this issue and does not wish to build the edit themselves, here's a version with the changes suggested by @Templarfreak implemented. Do note that this does remove the ability to use Refined Obsidian for Nether Portals, which I have never done.

https://mega.nz/file/zPZB0QwD#WcPOyFc15LJD7iR31QHjwysAGXcOUisTDHQWmnEpySk
I will not be providing support for this, unfortunately. I have only tested Mekanism-1.12.2-9.8.3.homebaked.jar, but here's a screenshot of a LiteLoader mod (Mine Little Pony) running, Mekanism Energy Cells, and a Nether Portal at the same time.

Update: I've discovered that Extra Foam For Liteloader by asie also patches this issue, completely negating the need to disable Refined Obsidian portals and not possibly requiring that you use a compiled version from some random user on GitHub.

https://www.curseforge.com/minecraft/mc-mods/extra-foam-for-liteloader

Probably use that instead.