Massive RAM Problems with 1.14

Hello there,

since I updated my server to 1.14 (using paper #122 now) I am struggling with a heavy impact RAM problem.
My Server keeps “collecting” RAM space until its full and then crashes because out of memory.
And the crashes are the baddest thing, because everytime some players lose their items and some of their latest buildings.

I want to figure out, what is causing this RAM collection and don’t know, what I can do…

What i did:
-> tested more RAM (Ram keeps collecting, but more RAM = More Uptime (now 26GB))
-> searching for some suspects:
----> What i found out: The Server ist getting every ~15sec about 500MB more RAM usage. And the more players are online, the faster the RAM gets full.
-> Updated all Plugins

My startup-Parameters:
java -Xms1024M -Xmx26000M -XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:MaxGCPauseMillis=100 -XX:+DisableExplicitGC -XX:TargetSurvivorRatio=90 -XX:G1NewSizePercent=50 -XX:G1MaxNewSizePercent=80 -XX:G1MixedGCLiveThresholdPercent=35 -XX:+AlwaysPreTouch -XX:+ParallelRefProcEnabled -jar server.jar

I installed “Spark” yesterday and when I use it i get some reports. Maybe you know what useful information i can get out of these…
Another thing I found out. Everytime Im creating a heapdump, my ram usage falls from maybe 20GB down to 7GB. (Heap summary)

pls halp D: