Well, I am starting to further understand what was going on.
Had guests all weekend so I could only get to the final stages of demolition today.
Tore up the rest of the affected tiles, pulled off the shower walls, pulled out the shower pan and popped up the platform. This is what I found below:
Now its time to snake it all, figure out a better solution for that cleanout, which is where all the accumulation seems to be coming from. Then reassemble.
What a pain, and what a relief all in one......
Unless I find something else is wrong as well.
Cheers
Cy