No, generally speaking, if you find that your old classmates or friends have blocked you, the possible reasons are:

The other person may want to have more private space and don't want his life to be paid too much attention.

There may be things you don't want to share, such as work and family.

There may be some negative emotions that I don't want to affect others.

You can try to communicate directly with your old classmates and ask why you choose to block your circle of friends. Of course, respect each other's choices and don't ask too much. If the relationship is good, you can ask the reason directly to avoid misunderstanding. If the relationship is average, so be it.