If the tank cools fast after being hot a vacuum forms that starves the engine of fuel causing a stall within a block or two. Even happened to me on a stock bike when brand new… usually after riding hard to get fully warm then parking it for a short time (store visit) before blasting off somewhere. While parked the engine heat goes into the tank which rapidly cools when you take off, forming a vacuum. Adding gas seems to help because you opened the tank and released the vacuum.
Not saying this is it but definitely something to keep in mind.