We issue each investor a monthly check for their % of each monthly mortgage payment. 

Can anyone recommend good companies to root cause  and implement solution to fix this issue?

The rates vary throughout the State because of the different millage rates and tax districts, but in Richland County for instance, the taxes essentially triple once it goes from legal resident to non legal residence. 

Investors obviously want their properties rented with no issues but they also want to be in the know and have a good line of communication when things come up.

There's a good chance the issue(s) you face has already been discussed and answered.Ask questions in the appropriate forum.

Our firm is planning on starting a Portal (legal term) next year on our roadmap because with $5M as the new threshold this really can move the needle for certain projects and sponsors.  

Seek legal advice, however, what I understand is that there are really two way to wholesale that is legal in the state of Arkansas.

There are guidelines and guardrails, but a challenging deal can have positives and a golden deal can have issues below the surface.

Then there were some issues with the inspection report that ruined 3 contracts prior to me getting involved.

A national buyer would review the BPO and maybe do some brief online research, but would not typically not know, as in your example, about the sewage issues or extent of interior rehab needed.