Cant open/edit number of Linked Entity dataflows. Error:"There was a problem opening your dataflow."

[Jords]

Dataflow that has been operational for months has just become unresponsive.  Im unable to edit or open the dataflow, with the error (at bottom)

Ive tried various browsers on multiple PCs - so nothing to do with cache - the dataflow is also inaccessable to datasets causing connected datasets to fail their refresh

This is one of three dataflows failing to open, the failing dataflows are all part of a Linked Entity chain  - the base dataflow opens fine but three dataflows above the base all fail to open, with similar errors to the one below.  (each dataflow referencing the previous one in the chain) The uppermost level is then connected to datasets (which are now failing to refresh)

We have similar parallel chains (10 in total) all with identical structures but connecting to different sources at the base level.  The other 9 are all operating correctly. 

Have even tried editing dataflow setting (in settings page) - but on applying changes get similar error

Something went wrong

There was a problem opening your dataflow.

Please try again later or contact support. If you contact support, please provide these details

Activity ID: a6a1f37b-1cba-4cb3-b5f0-ab7dac2665ac
Request ID: fda46e0b-4bc0-4c42-2839-aa37d09a3d3d
Correlation ID: 8d2c2b7c-2573-b4f3-05bc-8a3b9ca376e3
Status code: 400
Time: Sun Oct 03 2021 19:16:04 GMT+0100 (British Summer Time)
Service version: 13.0.16856.75
Client version: 2109.3.07961-train
Cluster URI: https://wabi-uk-south-redirect.analysis.windows.net/

this was first noticed in datasets connecting to this dataflow, which are failing to refresh as they also cannot access the dataflows, on editing the dataset the following error is shown 

[v-chuncz-msft]

@Jords 

The Link entities between dataflows works well for me. This might be a temporary issue, you may try again later.

[Jords]

@v-chuncz-msft 

it works well for me too. 

4 specific dataflows are failing to open out of hundreds of Link entities between dataflows operating successfully across our business. 

These dataflows are causing downstream dataflows and datasets to fail refresh