Why can't I break some blocks in creative mode?

Solution 1:

There probably are some invisible entities, as that'd only affect some blocks (which they stand on or next to) and spamclicking will eventually make you go around it. Check in spectator mode (/gamemode 3) and then find the source (which probably are command blocks)

Solution 2:

My explanations are 3:

1. You cant break stuff in creative while holding a sword
2. It might be a problem because of the java: It might malfunction or what, so i reccomend you reinstalling Minecraft
3. It might be a problem with your computer: When it is old, it has less than 2 MB of RAM (wich probably isnt it), its processor might be old and theese stuff.

I porbably didnt help you.