Dear @asmecher
Thank you for your support. We couldn’t make headway so reverted back to OJS 3.1.1.4
A fantastic idea came up that if we can actually move back, we can as well try to move further ahead.
Therefore we upgraded to the lastest stable release OJS 3.3.0.6.
After fixing every bit and pieces necessary, we started getting Slim Error on uploads to the site at any stage of the workflow
We found out that your suggestions on Error in submission - #2 by Angie_Jimenez about the absence of fileInfo worked fine.
Our journal site is up and running now.
Thanks and regards.