on the n8n Cloud Starter plan, you are limited to a maximum of 5 active workflows at a time. If you try to activate a sixth workflow, one of your other active workflows will automatically deactivat(Workflow active limit with Starter Plan?) This could explain why a workflow seems to deactivate itself when you activate another one.
If the user needs more than 5 active workflows, they would need to upgrade to a higher plan, combine logic into fewer workflows, or consider self-hosting for more flexibility