Akumar - I ran into this issue just last week. Let me explain:
We discovered this issue not while using Flow, but while using PowerApps, but it's the same issue. Flow, PowerApps, etc. - basically all of MS's PowerSuite Apps can only "talk to" SP Lists with 12 or fewer "Look-up" column Types.
If you're like me, at first was like wtfmate I only have a couple, like 5, but the reality is different... Here is a quote I found online: "Standard lookup columns, single-value managed metadata, multiple-value managed metadata, single-value people and group columns, and multiple-value people and group columns , Workflow Status , Created by , Modified by ( people ) are obviously counted as lookup columns .
Additionally following columns shows on list view also work as lookup columns , Name ( linked to Document) , Link (Edit to edit item) , Name ( linked to Document with edit menu), type ( icon linked to document)"
So, literally, OOtB a SharePoint list already uses up 2 of the possible 12 look-up columns allocated to you because of the "Created By" and "Modified By" columns - which you cannot delete.
You will need to remove all people-picker columns, managed metadata columns, etc. until you are down to 12 or less for Flow/PowerApps to be able to talk to your SP List.
The List I was trying to connect to in PowerApps had 14 people-picker columns + Created By + Modified By, meaning I had 16 "look-up" columns, so I had to get rid of 4 of my custom-built people-picker columns to connect to PowerApps.
Here is the article I think I got that quote from: https://powerusers.microsoft.com/t5/General-Discussion/SharePoint-too-many-lookup-columns-cause-quer...
