Assuming that you have adjusted the derailleur, it sounds like either a bent derailleur hanger or a defective freewheel. Grab the large cog on the freewheel and check it for free play when you rock it from side to side. There should be none or very little play. If the derailleur hanger is bent, replace it.

I have done 8.000 km on my Read City 5 plus. When I was younger I covered thousand of km per year on my 10 speed. I could not get a clean derailleur adjustment on my Rad  until I replaced the chain and freewheel at $6,000 km. It turns out the the freewheel was defective from the factory. Check the freewheel for side to side movement. There should be none. If there is replace the freewheel and chain.

The other thing that could cause this is a bent derailleur hanger. The bike may have fallen on its side.

I had the same issue with my left brake sensor and Rad sent me a complete brake assembly, lever, cable and calliper. They do not sell the individual parts. You may have to purchase a complete rear brake assembly.

The RadCity 5 plus is a heavy bike. Rad recommends 60 psi. The OEM tires have a max pressure of 65 lbs. I replaced the OEM tires with Continental Contact Urban tires at 6,000 km. Continental Contact Urbans are slick E50 rated tires with a maximum pressure of 70 psi. I run them at 70 psi as recomended by Continental.

I have done 5,500 km on my Rad City 5 Plus Step-through. I replaced the OEM tires with Continental Contact Urbans that are rated for E50. They are available at Sportscheck. What a difference. They are slick tires with very little rolling resistance. I can now cycle in one gear higher than with the OEM tires.

The cheap pedals that came with the bike gave out at 5,200 km. I replaced them with Raceface Chesters. They are also an improvement.

I have used the CYCEARTH "4 Pairs Bicycle Bike Disc Brake Pads for SRAM Avid Elixir E1 E3 E5 E7 E9 CR XO XX DB1 DB3 DB5 Nutt Oil Brake(Semi-Metallic/Sintered Metal)" brake pads from Amazon on my Rad City 5 Plus with great success.

https://www.amazon.ca/CYCEARTH-Bicycle-Elixir-Semi-Metallic-Sintered/dp/B08B1R9SK9/ref=sr_1_1_sspa?crid=2HZ6BQCWDJ34D&keywords=nutt+brake+pads&qid=1706075377&sprefix=nutt+brake+pads%2Caps%2C120&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

When I was younger, I was an active cyclist who put thousands of miles annually on my 10 speed  racing bike. I used 3 in 1 oil on my chain. 3 in 1 was designed for bicycle in 1895. It is still an excellent chain lube. That said, for my Radcity 5 plus step through, I use Muc Off dry lube. It is wax baed, does not attract dirt. 21st century bike have come a long way since 1895.

I have had a Rad City 5 Plus Step Through  for just over two years and I am approaching the 4,000 km mark. I am happy with it. It is a solid bike. As far as maintenance goes, I follow the manual routine maintenance schedule. So far, I have replaced the brake pads twice and bled the brakes. I had the front brake replaced under warranty as the motor disconnect was faulty. I upgraded the derailleur to a Shimano Acera, which in my mid performs better.

The Rad City 5 plus is a heavy bike and one must perform regular maintenance. I do not rely on bike shops for this. The information on the Rad web site maintenance  section is excellent.

In summary, the Rad City 5 Plus Step Through is excellent value for money.

I had a similar problem. It was caused by a faulty break lever. There was an issue with the motor disconnect, which stops the motor when the brakes are applied. Unplug the disconnect cables one at a time then try the throttle each time you unplug. Mine was caused by the front brake lever. Rad sent me a new complete front brake assembly which was simple to replace and adjust. If it it turns out that this is the problem you can keep cycling with the faulty motor disconnect unplugged. The motor stops Asher a couple of seconds.