This happened to me with the first mod I published. I went to edit it and was told I didn't have permission to remix it

I did figure out a way to have access to it again but it might not be something you want to try since you will lose all the stats for the creation.
First I unpublished the mod. Then I republished the original again using the same info except instead of selecting NO to
Can this be remixed I set it to YES. I immediately went to the original that I now had access to again and renamed it. After that I unpublished the copy that I allowed to be remixed.
To avoid it happening again I now add * at the end and beginning of all my creations. When I want to publish them I delete the *. Once published I delete the copy so I don't have duplicates of everything.