This is something that happened to me and had me stumped for awhile
I replaced the spark plug and unknown to me the electrode was loose
when I was holding it tip up it looked fine, but when I put it in no spark
looked thru everything couldn't find the problem, and I don't remember
what caused me to take a closer look at the spark plug but when I did
I could see when it was upside down the electrode slipped and closed the gap totally.
not saying this is your problem but........