Concurrent builds getting triggered on single build agent

We have been using TeamCity Enterprise 2018.2.2 (build 61245) and we have around 60+ teamcity agents.

Since a week time, we are getting to see the weird behavior with all the teamcity agents where it is allowing to two concurrent builds at a time despite we never enabled anything such setting explicitly. 

And obviously, the concurrent builds are causing conflicts utilizing the git workspace and inturn causing both the concurrent builds to fail.

Here is the outcome what i get to see with jcmd.

zxyzcity@h0012345: ~> $JAVA_HOME/bin/jcmd
75395 jetbrains.buildServer.agent.AgentMain -file ../conf/buildAgent.properties -launcher.version 61245
62678 sun.tools.jcmd.JCmd
75273 jetbrains.buildServer.agent.Launcher -ea -Xmx384m -Dteamcity_logs=../logs/ -Dlog4j.configuration=file:../conf/teamcity-agent-log4j.xml jetbrains.buildServer.agent.AgentMain -file ../conf/buildAgent.properties
75311 jetbrains.buildServer.agent.Launcher -ea -Xmx384m -Dteamcity_logs=../logs/ -Dlog4j.configuration=file:../conf/teamcity-agent-log4j.xml jetbrains.buildServer.agent.AgentMain -file ../conf/buildAgent.properties
75359 jetbrains.buildServer.agent.AgentMain -file ../conf/buildAgent.properties -launcher.version 61245

Please advise a way to troubleshoot further.