Thank you for your advice gentlemen but I have double checked that, and all my tracks start and stop times are OK.
I have uploaded many many songs in my band playlist and never had this problem before.
But after much head scratching I finally found what the problem was, and it is a strange one for sure.
I have two different versions of the same song (SUPERSTITION), played by two different artists (STEVIE WONDER AND STEVIE RAY VAUGHAN).
Each different version is in a different folder, but my mistake was naming the tracks in the folders the same way not realizing that Straxx won't discriminate by folder.
So I named the SW bass track "Superstition_Bass" and also named the SRV Bass track "Superstition_Bass", resulting in Straxx always using the first one uploaded in both versions even if they came from two different folders.
So the simple fix was for me to make sure the saved track names are different such as "Superstition_SW" and "Superstition_SRV" in both separate folders and that solved the problem.
Hopefully this could be useful for others to know.
Thanks!