Yes, I am seeing the same behavior you have explained. Going to try what you suggested to use “End Step” approach.
Seems like “Serial Loop” is a half cooked feature released a bit too early!! Working with Forms and Workflows still seems like we are in 90s.
Due to the issue I posted in this Use {{$.place.Holders}} as a part of JSONPath to read a variable in Workflows I had to create a workflow with individual steps instead of running them in the Loop with around 5 blocks per iteration and 18 iterations, which resulted in having around 90 blocks in the workflow. This resulted in the workflow to hang forever validating every time I clicked some item. Something that would take a minute would take 15 minutes as the page would not respond. Funnily when I downloaded the workflow it was just 40 kB, where as maximum limit is 400kB for the workflow json files. I can’t even imagine how would it handle workflows of size 400kB