You don't state what model Roku devices you have, nor the MiFi device in use. It's necessary information to see if your devices support 5 GHz, and/or 802.11ac. In general, 5 GHz can be much faster than 2.4 GHz.
What is your advertised/tested Internet speed on your MiFi? Are you playing 4K media, or HD?
Sometimes a device can be too close to the WiFi radio. The radio wavelength even at 2.4 GHz is measured in inches, and at 5 GHz in fractions of an inch. Sometimes you can move one or the other just a little bit and make a major difference.
OK, next thing to try. In the Roku settings menu, under System/Advanced system settings, there's a network reset function. This deletes all saved network connection settings. Sometimes they get something out of whack in those settings, and by resetting them it starts working again. It doesn't delete anything else from your Roku, so no need to log into sites again.
That seems to have done the trick. I’ve been cursing the **bleep** things for days now. Thank you very much. Unlike the one person who stated that Roku’s support sucks, I’m very pleased with it. Thank you very much for your help.
Well, I'm not Roku support. I'm just another user like yourself. Perhaps a little more experienced is all.
I can confirm that the network reset worked on my hisense roku tv! This happened for the first time just now.. I have had the jetpack for a few days now and was worried..does this happen often using the jetpack? Id like to know what im getting into..
Not particularly common for any specific device. It's just the first thing to try when you're having network connectivity issues. Glad it worked.