Yep, all they did was sending a replacement tube.

It was the front tire. Luckily my tube had only a small hole, which I patched. After making sure the rim strip is centered and covers all the holes properly, I carefully threaded the deflated tube in, making sure it's centered too and the strip stayed in place everywhere. Then inflated it to 50 psi and was a happy e-bike commuter (7 miles one way) for two weeks until I also got the safety notice e-mail.

At the time I didn't anticipate the risk of this causing the tube to rupture or flatten quickly, and my rear tire hadn't deflated at all, so I didn't check it. Will do that next.

I've never seen a rim with a loose rim strip. Looking forward to their solution...

FWIW, the issue mentioned in the Safety Notice (a misaligned rim strip) caused my front tube to be punctured two weeks ago (one week after delivery) apparently by one of the spoke screw heads (see photos). Luckily, it only slowly flattened the tube.

I sent the following support ticket to RPB on August 19:
"Hi,
after 4 days of riding the new Radwagon 4 the front wheel flattened, which prevented me from getting home from work. I had to take a Lyft for $25.
Upon closer inspection, it turns out that the tube was punctured "internally" by the rim itself. Specifically, the liner that apparently is supposed to cover the spoke screw holes was not properly centered, thus exposing some of the screw heads, one of which punctured the tube.
Since the whole tire came pre-assembled, and I only inflated it to the recommended 50 PSI, the problem causing the flat tire existing already at time of shipment. So could you provide me a matching replacement tube?
Thanks,
Timo"

Their reply on Aug 24 only contained:
"Hello,
I have ordered you a replacement tube 906896"

The tube arrived this week.