Self-setting successCount on a command block leads to a crash. The command blocks's "previous output" is not wiped with the application. The command block fills up, leads to crash.
blockdata ~ ~ ~ {SuccessCount:1}
[22:05:25] Block data updated to: {Command:"blockdata ~ ~ ~ {SuccessCount:1}",id:"Control",TrackOutput:1b,LastOutput:"{"extra":[{"translate":"commands.blockdata.success","with":["{Command:\"blockdata ~ ~ ~ {SuccessCount:1}\",id:\"Control\",TrackOutput:1b,CustomName:\"@\",SuccessCount:1,z:-74,y:1,x:663,}"]}],"text":"[22:05:09] "}",CustomName:"@",SuccessCount:1,z:-74,y:1,x:663,}
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Update: Setting a command block's command uning Blockdata also does this.