I just reproduced that again. And this time I was able to find this in the log (which was tremendous in size)
W0525 17:53:10.405345 20 log.go:36] [Compactor: 2] LOG Compact FAILED with error: sync p/MANIFEST: file already closed: {span:0xc009f4bd80 compactorId:2 t:{baseLevel:3 targetSz:[0 10485760 10485760 10485760 80759979 807599799 8075997999] fileSz:[67108864 2097152 2097152 2097152 4194304 8388608 16777216]} p:{level:4 score:1.7191355138911069 adjusted:1.4460537330498309 dropPrefixes:[] t:{baseLevel:3 targetSz:[0 10485760 10485760 10485760 80759979 807599799 8075997999] fileSz:[67108864 2097152 2097152 2097152 4194304 8388608 16777216]}} thisLevel:0xc00042d800 nextLevel:0xc00042d860 top:[0xc00a2bf140] bot:[0xc024aaa480] thisRange:{left:[0 0 0 0 0 0 0 0 0 0 17 101 98 97 121 46 108 105 115 116 105 110 103 46 110 97 109 101 2 8 49 44 50 44 51 44 52 44 53 44 54 0 0 0 0 0 0 0 0] right:[0 0 0 0 0 0 0 0 0 0 17 101 98 97 121 46 108 105 115 116 105 110 103 46 110 97 109 101 2 8 55 255 255 255 255 255 255 255 255] inf:false size:0} nextRange:{left:[0 0 0 0 0 0 0 0 0 0 17 101 98 97 121 46 108 105 115 116 105 110 103 46 110 97 109 101 2 8 49 44 50 0 0 0 0 0 0 0 0] right:[0 0 0 0 0 0 0 0 0 0 17 101 98 97 121 46 108 105 115 116 105 110 103 46 110 97 109 101 2 8 97 110 103 101 108 255 255 255 255 255 255 255 255] inf:false size:0} splits:[] thisSize:2277394 dropPrefixes:[]}
W0525 17:53:10.405416 20 log.go:36] While running doCompact: sync p/MANIFEST: file already closed