Wanted to add that I too am having the same issue using search, in modern view. We have a list with over 4,000 items. If the users scrolls through the list, or uses the filter by column option, then they can select the item and start a flow (either via the ribbon, or via a column I have formatted to start a flow). However, if they use search, they can select the item but the flow option in the ribbon is no longer available. And, the button in the formatted column is clickable, but does NOT start the flow.
Maybe this post should be changed back to unsolved, as I am able to recreate this issue today.
FLOW OPTION IS AVAILABLE FOR SELECTED ITEM (FOUND WITHOUT USING SEARCH)

FLOW OPTION IS NOT AVAILABLE FOR SAME SELECTED ITEM, WHEN USER SEARCHES FIRST
