GridFieldManyRelationHandler requires the GridField to have a RelationList

[spacebiscuit]

I have created two of my own content blocks:

class MyContentBlock extends ContentBlock{
class TestimonialContentBlock extends MyContentBlock{

All worked fine and as expected. I then added a 3rd block

class SidebarContentBlock extends MyContentBlock{

Then when I went to add a CB in the model admin I get:

ERROR [User Warning]: GridFieldManyRelationHandler requires the GridField to have a RelationList. Got a UnsavedRelationList instead.
IN GET /admin/block-admin/Block/EditForm/field/Block/add-multi-class/TestimonialContentBlock

Please help - thanks!

[sheadawson]

Hmm that's stange. Can you do a dev/build?flush=1 and let me know if the issue persists