error with getEvonodesProposedEpochBlocksByIds with epoch<7

[p-m]

Hello,
I would like to get the count for any epoch, for example epoch 6.
I use this command:

grpcurl -proto node_modules/@dashevo/dapi-grpc/protos/platform/v0/platform.proto \
    -d '{"v0": {"ids": ["XXX"], "epoch": 6}}' 1.2.3.4:443 \
    org.dash.platform.dapi.v0.Platform/getEvonodesProposedEpochBlocksByIds

Expected Behavior: Get the count.

Current Behavior: Error message:

ERROR:
  Code: Internal
  Message: query: storage: grovedb: path parent layer not found: could not get key for parent of subtree optional no tx: path key not found: key not found in Merk for get from storage: 6d

TIA for any help to get the count for any epoch, Peter