After today's update, there are some fish on floor 2 and 4 that are listed as can't catch/minimum rod prism, even though I have all the rods (and divine rod currently equipped to everyone). The floor 6 fish that require minimum rod prism *are* listed as catchable though.
Just checking, but perhaps you can verify, are you certain it isn't a rarity issue? If you have a hook attached to your rod that increases your luck (say for example to a +75%) it could result in a fish that is too low rarity (say for example a fish with a 7.9% catch rate as a common fish) to have too low of a rate to be catchable. When this happens, if you equip a hook with a lower luck value, you can increase the chance of catching uncatchable or incredibly low odds (0.0078% chance) low rarity fish.
If this is NOT your issue, however, it might be helpful to provide which fish they are so it could be looked into. Would you mind doing that? I'm sure it would be appreciated.