This also happens if you put 6 or more tnt minecarts in a row faced with dispensers with a block of lava inbetween. The first 5 will detonate all at once but the 6th or more will detonate seemingly after a random delay despite being hit at the same time with burning arrows arrows.
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this design will detonate all 3 minecarts placed on the rails but expanded it behaves as I described above.
Ossbourne
This also happens if you put 6 or more tnt minecarts in a row faced with dispensers with a block of lava inbetween. The first 5 will detonate all at once but the 6th or more will detonate seemingly after a random delay despite being hit at the same time with burning arrows arrows.
this design will detonate all 3 minecarts placed on the rails but expanded it behaves as I described above.