I found the solution to this error. This was the result of RConnect not being updated to support new versions of Streamlit (> 0.78). Now I am able to deploy my Streamlit app (created with version 0.88) successfully on RConnect version 1.9.0.
There are still some issues unrelated to deployment that I am trying to figure out:

Downloading a file to user’s default Downloads folder works in my private environment but not in the deployed version with RConnect.
Incorporating images/ icons into my deployed Streamlit app.

Any help for above two issues is greatly appreciated.