Post your router model number as most Verizon Home 4g LTE setups are currently using both the older Askey RTL108 and the newer Netgear MBR LTE routers and their settings/locations will be a little different. (Although it may say Verizon on the router, you should see some "Model Number" on the stickers which will tell us which router you actually have.
Some Verizon customers are having trouble with the IPv6 protocol used by Verizon when enabled. I haven't seen anything in particular related to the 4g Home LTE routers but is affecting their 5g, Fios, and hotspot device networks. As such, one troubleshooting step would be to disable IPv6 if you are currently set to IPv4/IPv6 (or if you have IPv6 toggled to ON position in settings). If for some reason you need to navigate to an IPv6 address, you will receive a message that the site is unreachable, so you can always toggle to ON as needed.
@renojim 's advice regarding the DFS channels is likely spot on if you have the newer 4g router.
The Netgear 4g LTE routers (depending on model number) are capable of using DFS channels (52-140) which Roku cannot see or use so would cause the Roku to disconnect and be forced to use the 2.4ghz band if your 5ghz band Channel Selection is set to Auto. As such, will need to manually assign a 5ghz channel to 36-48 or 149-161 on the 5ghz band and change the 2.4ghz band to use mode b/g/n if you notice the Roku is having difficulty connecting to the the 2.4ghz band.
The Askey RTL108 does not have DFS capability so this would not be an issue. Additionally, the Roku should be able to connect to mode g/n on this router for the 2.4ghz band, but can also try b/g/n. The only real reason the Roku would be losing connection on the 5ghz band of the RTL108 is due to interference. This was really the only complaint of the older router was its strength and prone to interference/channel crowding. Suggestion on this router would be try different channel numbers. (can optimize a bit more by downloading a free wifi analyzer to your phone that may help you find a lesser crowded channel).
Again, post back with actual model numbers you see on the router so can tailor suggestions.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941