'PACK' is not a valid git packet prefix - IllegalArgumentException in debug logs

2018-09-03 16:52:08,018 DEBUG [io-pump:thread-7] admin @1IU8VG1x1011x113x0 0:0:0:0:0:0:0:1 "POST /scm/projkey/reposlug.git/git-receive-pack HTTP/1.1" c.a.b.s.g.p.AnalyzingInputStream Error analyzing input
java.lang.IllegalArgumentException: 'PACK' is not a valid git packet prefix
    at com.atlassian.bitbucket.scm.git.protocol.GitPacketStream.parsePacketSize(GitPacketStream.java:204)
    at com.atlassian.bitbucket.scm.git.protocol.GitPacketStream.readPacketPrefix(GitPacketStream.java:223)
    at com.atlassian.bitbucket.scm.git.protocol.GitPacketStream.append(GitPacketStream.java:109)
    at com.atlassian.bitbucket.scm.git.protocol.GitPacketStreamAnalyzer.process(GitPacketStreamAnalyzer.java:24)
    at com.atlassian.bitbucket.scm.git.protocol.AnalyzingInputStream.analyze(AnalyzingInputStream.java:51)
    at com.atlassian.bitbucket.scm.git.protocol.AnalyzingInputStream.read(AnalyzingInputStream.java:40)
    at java.io.FilterInputStream.read(FilterInputStream.java:107)
    at com.atlassian.bitbucket.util.IoUtils.copy(IoUtils.java:106)
    at com.atlassian.bitbucket.web.cgi.BaseCgiHandler.copyStream(BaseCgiHandler.java:32)
    at com.atlassian.bitbucket.web.cgi.CgiInputHandler.process(CgiInputHandler.java:26)
    at com.atlassian.bitbucket.scm.SummarizingProcessHandler$DelegatingOutputStreamHandler.process(SummarizingProcessHandler.java:216)
    at com.atlassian.bitbucket.scm.SummarizingProcessHandler.provideInput(SummarizingProcessHandler.java:94)
    at com.atlassian.utils.process.ExternalProcessImpl$StdinHandler.handle(ExternalProcessImpl.java:770)
    at com.atlassian.utils.process.ExternalProcessImpl$HandlerLatchedRunnable.doTask(ExternalProcessImpl.java:731)
    at com.atlassian.utils.process.LatchedRunnable.run(LatchedRunnable.java:158)
    at com.atlassian.stash.internal.concurrent.DefaultTransferableStateManager$StateTransferringRunnable.run(DefaultTransferableStateManager.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.lang.Thread.run(Thread.java:745)
    ... 1 frame trimmed