Tried to promote an Unmanaged solution from Dev to Prod using Pipelines and received this error message:

Tried to delete the solution on the Production and got continued issues.

Cannot immediate resolve, need help with steps to get this 100%
Also tried to Export and Import with the same issue.
Per this link: https://powerusers.microsoft.com/t5/Using-Flows/Solution-failed-to-import-Solution-Upgrade-action-failed-after/td-p/1350023
It was recommended to:
After working with Microsoft Support, they had us delete the existing solution, go into the solution called "Default Solution" within that environment, delete all of the connection references and custom connector connections we had and then re-import. It worked for us after that. Not sure if this would help you.
Unfortunately, we have other apps and don't want to impact the production of the other apps. Need a more tactical solution to help complete our needs.