I have the same problem. The old one in the living room works fine but the new one in the bedroom FF is too fast but it used to work fine until a few of months ago. It mainly (only) happens on Amazon Prime video so I called them and they of course sent me to Roku's phone number which of course "due to the virus" BS excuse,,, they have NO live customer support people BUY Hey, even my bank and credit card people and VONS store have customer support people, most working from home but hey, not Roku... and their support is zero help too (tells you to buy another remote)... a if...
I am not happy at all is saying very little. I think it is a Roku problem...