There's not really many good ways to test.
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You could use the cmd.exe ping -t command to ping the ravenloft server itself repeatedly with small packets of info as a pseudo connection test and leave that on another monitor, and if it starts spiking in duration for packets returned and packet loss, examine your Resource Monitors' incoming and outgoing data rates.
If there's an offending program thats flooding your bandwidth that only occurs periodically that would be a way to pick it up, whether it is automatic updates or some other intermittent service, as long as you know how to read it.
Task Manager & Resource Monitor everyone should learn how to navigate at some point when using computers.
If you find a program there that really shouldnt be there that keeps coming back when you reboot your computer, you'll have to check your startup programs list and disable it from booting on startup, or open your Settings registry and change the program from "Automatic" to "Manual" if it isnt a core component of your computer.
If someone else is on your network they could be crashing the bandwidth too with their own problems, I had to seriously correct my dads' laptop with all the startup Microsoft junk our internet connection couldnt handle just continuously crashing both his computers' ram and our bandwidth.
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The nwnravenloft forums as a browser issue shouldn't have anything to do with lags or disconnects in the game itself. Chrome issues usually stem from cookies that need clearing or extensions / toolbars that have been installed that really shouldn't have been.
Some toolbars kids pick up while browsing the net aren't particularly malicious at first glance, inserting advertisements into pages that shouldn't have advertisements or trying to do bitcoin mining with your "extra resources" and this can cause conflict with web pages using security protocols, as well as make one more prone to picking up an actual virus from advertisement pages that may provoke automatic downloads or running of scripts.
Or, both issues might be stemming from ones internet adapter settings being set up incorrectly for the type of internet service being provided. You'd have to check your proxy settings to see if it has been set up correctly or if its still referencing old or outdated addresses / ports or if someone turned it off from automatically detecting settings.
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Not really many good ways to test someones issue from the limited information in a post. So many things to check and one has to learn how to both find, read and interpret the information if they want to be able to resolve it, and so many ways to mess up the computer.
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There was also a series of steps one of the discord users named "Symphony" posted under the ravenloft discord thread of nwn tech issues I think that followed a similar framework of following tests step by step to self-diagnose the issue, if you can find that that'd be another thing to run through.