Check your virus scanner settings.Some virus scanners have the option to scan archives when extracting java archives (.jar files) which FME 2017 extracts on start up and when Web Connections are access for the first time so it is likely these problems are related.

Try disabling archive scanning to see if it makes a difference.If so consider either whitelisting the FME install directory, or, the fmeworkbench.exe process itself.Here is an example of how to approach this in McAfee.As pointed out in the link, disabling archive scanning is fairly low risk, however, it will all depend on the policies of your IT security department as to the best approach on this.