You need to clear the previous start command via override config:
[Service]
ExecStart=
ExecStart=/usr/bin/java -Xmx1024m -jar komga.jar
Else the added one is interpreted as second command, which is only allowed in combination with specific service types. As the other directives/sections are untouched, you don’t need to uncomment them.
We should add this info to the initial template file when the “Edit” option is used 
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