First noticed this issue with the 1.16.4 update a few months back. Did not find an issue describing this specific problem.
The brewing stand will not accept potions of maximum duration (potions with redstone applied) after they have been removed from the stand.
I have attached my current build information and a video showing the issue.
Steps to Reproduce:
Place water bottles in the brewing stand (already has sufficient blaze powder)
Brew any potion that can have the duration extended with redstone.
Brew potions with redstone.
Remove potions from brewing stand.
Attempt to place back into the brewing stand to transform into splash potions using gunpowder.
Failure: unable to place maximum duration potions back into the stand...