We received reports of existing Jenkins masters failing to send build jobs to Windows 2016/2019 slaves upon only upgrading ec2-plugin from 220.127.116.11 to 1.50.3. We confirmed this by launching a fresh master, applying all updates except ec2-plugin (leaving it at 18.104.22.168). Then we ran multiple Windows test jobs and saw Windows slaves launched and execute the jobs.
We then performed only the update of ec2-plugin from 22.214.171.124 to 1.50.3 (nothing else changed) and tried to re-run our test Windows jobs. This time the Windows slaves did not connect, but reported as "offline" even though I could see they were running in AWS Console, also I could RDP in, also they ran a build just minutes earlier at previous version.
Instead, Jenkins master with the latest ec2-plugin started launching new instances, but never connecting resulting in 10s of instances launched but not used. Required manual cleanup.