I have followed all the instructions here https://www.drupal.org/node/2598914
I'm developing a module with a block, and when I went to the Block Layout page and clicked "Place Block", the list of blocks did not come up due to an error in my code. I edited the code and was sure it was correct, yet it still didn't work. So I tried doing "drush cr" just in case the cache wasn't really disabled ... and that made it work.
So it seems to me that the cache has not been disabled by following those instructions. Is there something missing?
Edit: This has happened again when I have made new changes, even after the plugin has successfully loaded. It happens when when I make any changes to
src/Plugin/Derivative/Foo.php (inside my module). Those changes aren't picked up until I manually cache rebuild