This sounds like Grounded 2 — the buggies going "downed" and returning to their nest to auto-revive matches what you're describing, so the "Not Available" status might just mean they're mid-revive rather than actually stuck. That said, buggies not coming back out even after you've cleared/reassigned summon spots and reloaded sounds like it's crossed into genuine save-corruption territory, so I'd report it directly on the Grounded 2 official Discord or Obsidian's bug tracker with your save file — this kind of persistent state bug across a restart usually needs a dev-side fix, not a player workaround.