Teamviewer disconnects immediately after connection

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This behavior started two weeks ago which I am trying to troubleshoot.

Machine A on Lan connects to Machine B external: connection drops directly

Machine C on Lan connects to Machine B external: connection OK.

Machine C on Lan connects to Machine A on Lan: connection drops directly

Machine A on Lan connects to Machine C on Lan: connection drops directly

Machine D on Lan connects to Machine C on Lan: connection drops directly

Machine D on Lan connects to Machine A on Lan: connection OK.

No settings changed on local Firewall.

No settings changed on company Firewall and Proxy.


Any idea what to check more?

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