Found a bug with disappearing blocks. I'm not sure if it is caused by this issue or the conversion to json, but this is the first time a noticed the bug.
Go to https://pi-integrated.e-activesites.nl/test-page
Add two columns
Put the block "Zoeken" in the left column
Put the block "Zoekresultaat" in the right column
--> blocks are saved
--> blocks disappeared
All blocks in columns seem to disappear after editing