I have a JMH that acts like this, where the slower 854.109 ms/op is more common.

# Run progress: 0.00% complete, ETA 00:02:30
# Fork: 1 of 5
# Warmup Iteration 1: 441.124 ms/op
# Warmup Iteration 2: 415.528 ms/op
Iteration 1: 385.257 ms/op

# Run progress: 20.00% complete, ETA 00:02:32
# Fork: 2 of 5
# Warmup Iteration 1: 854.109 ms/op
# Warmup Iteration 2: 827.729 ms/op
Iteration 1: 828.441 ms/op

With -XX:-TieredCompilation, the score is steady in the faster 400 ms/op.

I'm running 12-b19 but I can cause this going back to jdk-10 too.