Three scenarios:
Gaming only - no problem.
Gaming while Discord is running - no problem.
Gaming while Discord is running and joining a Discord call - PROBLEM.
Feel free to add to or otherwise edit my scenarios as applicable.
There are a number of ways to delve into the problem(s) a bit more.
Take a look in Reliability History/Monitor. Do you see any error codes, warnings, or even informational events being captured just before or at the time of the keyboard's keys getting stuck.?
Other tools that can be used are Task Manager, Resource Monitor, Process Explorer. Anyone or all three tools (use them only one at a time) may reveal some change when the keys start to stick.
May take some trial and error to set up and be able to watch the tool to determine what happens while gaming in Discord, joining a call, and the keys stick.
Overall, if there are no readily apparent problems then reinstall Discord. That might resolve the problem.