I try to create a process, and get the above warning.
I retrieved the following article : https://releasenotes.docs.salesforce.com/en-us/winter19/release-notes/rn_forcecom_flow_design_num_processes.htm


But the one that already exists only works when records are being created, while I now have the requirement for a process that also acts when record is being edited. I presume I'm obliged to create a new one then?? 

I have tried to complete this trailhead, but keep getting this error message below.  Can anyone help me figure out what this means and how to fix it?  Thank you!
'Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Account number must be 8 characters long.: []'