Suddenly, there is a delay when pressing buttons on just one of my devices.

I have a Harmony Smart Control Hub & Remote. Suddenly, there is a delay every time I press a button on my Harmony remote with one of my devices. It's my Roku Ultra (2016). Everything has been working fine for years, but now, once I am in my Roku activity, there is a 2-3 second delay every time I press a button on the remote. I have other activities/devices associated with the same hub/remote and they work fine, like always. It's just the Roku with the sudden delay issues. I've tried restarting the hub, restarting the Roku, restarting my Cable modem & my router, changing from Wired to Wireless connection in the Roku settings. I tried changing the delay settings within the Harmony app, made sure firmware is up to date, even put in new batteries in the remote - nothing has worked. When trying the remote function on the Harmony app with the Roku, I get the same delay issue. If it's a network issue, I have no idea what to do, and why are my other activities/devices working just fine using the same network, hub and remote but within the Roku activity, it suddenly has the delay? When I use the original Roku remote with the Roku, it works perfectly, the way my Harmony remote used to with the Roku. Any suggestions? I have no idea how this could suddenly happen when everything was fine for ages.