Just for an experiment, can you try reducing your spark plug gaps?
I have seen healthy fat blue sparks on removed plugs, but no fire when fitted. Compression pressure can be high enough to prevent a spark jumping the gap. The higher the air pressure at the plug, and the larger the plug gap, the higher the voltage needed to spark.
Maybe the new gaskets have raised the compression pressure?
I've seen a 1909 Fairbanks Morse engine run with a plug gap of 0.15mm (0.006"), but not with 0.63mm (0.025"). The weak spark from the magneto sparked a 0.6mm plug gap fine when removed.
A V11 runs well with a spark plug gap of 0.7mm (0.028"), with 9.8:1 CR, because the factory electronic ignition delivers high voltage with high energy to each plug.
Nippon Denso has some basic information on plug gap and compression pressure:
Conditions that affect the discharge voltage | Spark and Ignition | Basic Knowledge | SPARK PLUG | Automotive Service Parts and Accessories | DENSO Global Website