I've dealt with quite a few this year that had debris sticking in the fuel pickup tubes and fuel lines. The pickup tubes & lines had to be blown clear with shop air or replaced.
Grass clippings, dust and/or debris/water from a dirty fuel can often takes years to build up in a fuel tank and then get sucked in. This stuff slowly blocks the fuel flow and starves the engine. After it shuts down and sits for a while, the debris relaxes in the lines until the engine is run again. The problem keeps repeating itself.
