My Roku Ultra which I just got last year was and has been continually showing between 97 and 114m.
Then all my speed went to utter **bleep** and has been down in the 40s or even 30s and 20s now.
I didn't change or adjust a single thing and I didn't do my anything at all to my router and modem.
And yes I have unplugged it and turned off the power and disconnected the cable from the wall multiple times over the last few days and that doesn't do anything.
Just after this last update it is absolute **bleep** speed. Thanks a lot Roku. There is absolutely zero accountability with this company ever.
My laptop speed is and was fine and there isn't anything wrong with my Comcast cable and I have run multiple speed tests on my laptop and they all come back great and as usual.
Once again, just like with the entire HBO thing last year, it is Roku and ONLY Roku which did this.
What is absolutely pathetic is the entire reason why I bought my new 2021 Ultra was because my old stick wouldn't work anymore after Roku did that big update last year which screwed up everybody's HBO.
You didnt mention which Ultra model, but if you got it last year its most likely a 4800, which has a better WiFi chipset than previous Ultra models (and supports much higher 5Ghz bonded channel speeds), and assuming you have firmware version 10.5.0-4208, you should see speeds around 200Mbps (assuming a 5Ghz AC connection) when checking the connection via Settings/Network/Check connection.
You say you didnt change anything to your modem and router/gateway; however, that doesnt mean they didnt change themselves (via auto-updating), via both firmware and/or settings updates, especially when managed by Comcast (they control the firmware updates/settings for the modem at least), and possibly the router/gateway too, if its Comcast provided).
In addition to that, the 2.4/5Ghz WiFi channel assignments can/do change as well (if not manually configured), which can result in degraded performance if currently on a highly used channel (nearby/neighbor's devices on the same channel).
1) Make sure you have separate 2.4Ghz and 5Ghz SSIDs, and that channel bonding/bandwidth is set to Auto or 40/80/160.
2) Verify your Ultra is connecting via 5Ghz.
3) Verify the 5Ghz channel isnt overused/overlapped (e.g. use WiFi Analyzer on an Android phone/tablet for this)
4) Manually configure 24/5Ghz channels to unused/underused ones in your modem/router/gateway.