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I replaced the old script, but I have the same error.   On first run of UnityScene, the S7 Interface component is being disabled.  If I enabled it in run mode, that's when the cpu quickly winds up to 100%       - I'm be no means an expert on this, but could it be that you need to implement IDisposable into S7Client, and wrap the "Client = new S7Client" like so:   using(var Client = new S7Client), so that the garbage collector can take care of it ?