Have you checked if you are in Adventure mode? If so, change to Survival or Creative Mode.

He/She/It is probably trying to break locked blocks. They can't be broken, sorry!

Maybe... Are you trying to Break blocks inside a Dungeon, or on the Dungeon Tower (the big tower with dungeon blocks)?

I believe i have the same issue but only when i reach a certain area. it makes all blocks other than tall grass act like how you can't break locked blocks except it spreads to all blocks when i reach an "invisible barrier". the only cure is to leave and return. at least that's all i've found so far.

I have experienced that issue too, the invisible area one, but it does not go away... I could use a little help in the understanding of this

Guys, I wish I could help you with this problem but I never experienced it nor know how to fix it. It seems like a bug related to normal block chuncks being recognized as dungeon block chunks, but I don't know how to fix it...