Do you have more than one texture pack running? Maybe a conflict where both are being called to the same block? Just throwing things out here - not overly familiar with texture packs beyond the basics. All else fails, delete the texture pack and redownload to rule out a corrupted file on that side.
One of the reasons I moved away from the Curse/Twitch launcher was the inability to remove the outdated and irrelevant junk it throws into the Java arguments. Not cool that if you add a custom line that goes against what it wants, it simply overrules your decision with its own crap. No thanks. I need those custom arguments to squeeze every ounce of performance out of this old franken-tater.
Yes, I'm using many texture packs. But, the way they work is a priority system. So, if you have multiple packs, the highest one will take precedence. Chroma hills is, all things considered, the best HD texture pack for vanilla. There are more realistic packs, higher res packs and obviously this is super subjective. I'm saying if I worked for Minecraft Teen Beat Magazine and I were to review texture packs, this would be my highest rated one. And just like the Natural Texture pack with the C++ versions, it's been seared into my identity of modded Minecraft and I can't play without it.
But, it makes the modded stuff look bad in contrast. So, I fill in the blanks with whatever I can find. Second layer here, due to it having a style that isn't far off from Chroma Hills, is Soartex fanver modded. But, that's missing a lot if mods, including my two favorites, enderIO and Actually Additions. So, I fill that in with BD craft, which has most of Beyond covered and even though I'm not a huge fan of the style, actually works ok as a supplemental piece.
I will migrate this thing over to MultiMC eventually. If it's not curse being curse, I haven't ruled out continuum shaders just yet. I can't let it go, though. I need to get these all working together and stable, no matter what it takes.