This has been a persistent bug/problem in lookout for years.
Virtual serial ports with slow communication or no response. Every vendor we have tried (Lantronix, Moxa, Digi, ICP-DAS, etc.) does exactly the same thing in Lookout. If lookout supported IP-Tunnel, as many softwares do now, it would likely help significantly. But alas, Lookout is not being updated and this will not happen.
Also, be aware that trying a Modbus Serial-TCP gateway will present more problems int he way Lookout handles connections and will crash on a commfail, not hang: Crash! If there is more than one serial device on the IP address, Lookout crashed quite often on poor communications (think radio).
Good luck
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