The bug
When you get a potion as junk from fishing, it is "uncraftable" because it has no Potion tag.
How to reproduce
Summon for example a mob with the junk loot table and kill it until you get the potion.
/summon villager ~ ~ ~ {Health:0.1f,DeathLootTable:"gameplay/fishing/junk"}The reason
The loot table minecraft:gameplay/fishing/junk.json is not setting the NBT for the potion.
Can confirm , I got the uncraftable potion first try and it has the texture of a strenght potion , But this might be a placeholder for a future drop , keep that in mind