Activating the Pack in Your World
Having the pack installed is only the first step; Minecraft will not apply its fixes until you activate it in your settings. If vertical slabs created with Autoslabs still show missing textures or broken block faces, open the pause menu by pressing Esc, click Options, and select Resource Packs. Look in the left-hand Available column for Autoslabs Compat Resource Pack. Hover over its icon and click the right-facing arrow to move it into the Selected column on the right.
Setting the Correct Load Order
Minecraft applies resource packs from bottom to top, meaning packs higher in the list override everything beneath them. Because this pack patches missing texture problems across Autoslabs and your installed decoration mods, it must sit above the built-in Mod Resources entry. Use the up arrow on the pack's icon to raise it above Mod Resources in the Selected column. Return to your world and inspect your placed vertical slabs from BetterNether, BetterEnd, Hearth and Home, Promenade, or Supplementaries; their block faces will now render with clean, consistent textures instead of broken visuals.