Same problem here, I open an existing module, save and then it's empty. It's both getting emptied in the administrator section AND the front-end.
I've dug around a bit in the database comparing 2 modules, one broken and one that I didn't save therefore functionnal. There are 2 tables involved, _modules and _sppagebuilder. To what I can understand in the _sppagebuilder table, the column view_id refers to the id of _modules and that's how the link is made between the rows of those tables (and also the titles match).
Functionnal
- in
_modules the column params is short, a bit info about layout, moduleclass_sfx, cache and such.
- in
_sppagebuilder the column text contains the content of the module that is expected.
Broken
- in
_modules the column params is long, the content is now here! The JSON begins with content!
- in
_sppagebuilder the column text is completely empty.
I hope the solution will be found quickly and that the fix will be cleaver enough to support both cases or maybe a tool to fix the mess.