Unfortunately you are seeing some of the issues that prompted the (new) Dgraph team to revert to v21.03. The @latest supported release is v22.0.1 which is based on v21.03. v21.12 is discontinued and unsupported. There were performance improvements introduced in v21.12 that were impressive, but also introduced some instability.
I recommend that you move to v22. This will require and export/import. Also, be aware some features introduced in v21.12 are not v22. I’m happy to help where I can but it seems like you’re already quite adept at export/import!