I am currently running a dedicated server for snapshot 18w43c, and have noticed a common pattern.
When no players are online, and one connects to the server, a number of rapid lighting strikes occurs simultaneously, causing massive fires that cause large amounts of damage to the naturally generated terrain.
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I just had something like this happen to me when I joined a dedicated vanilla server I am running in 1.14 (was only player logging on and did sound like multiple strikes at once. I will see if I can reproduce the bug.
edit: I was able to reproduce the bug in 1.14 by starting a storm with commands on a server, leaving the server, ending the storm from the server console after about a minute, and then logging back in.
Forward resolving to MC-152908.
Cannot reproduce in 18w47b. Please check if that's still an issue for you.