I'm a little rusty with the terminology, but in a blockchain, the canonical current block is the one that has the greatest amount of proof of work (I think they call this the heaviest chain). Typically, each new block is the descendant of the most recent block. But it is possible to create a heavier chain from an earlier block. This invalidates any transactions on what was previously known to be the heaviest chain, and is called a reorg.

The farther back, the less likely a reorg is, so to have a reorg that invalidates is blocks is extremely unusual.

If one entity has a majority of the hash power, they gain the ability to try to force reorgs with a likelihood that increases with their advantage in hash power.

I typed all this before realizing I could have recommend you ask an LLM, and it probably would have given you a better answer.