I've had a couple of connection issues with my Shimano E8000 during the past year. I encountered both problems at different times while riding a rougher paved road, so I think vibration caused it. A phone call to my trike dealer, in each case, gave me the information so I could fix the malfunctions.
The first problem (encountered after 6 months) was the motor would shut off and the display showed E-10 and had to be rebooted, which is a connectivity issue. There are two treatments for this: 1) apply dielectric grease to the battery cradle (or bracket) electric contacts. This may temporarily solve the problem, but the real fix will be:
2) remove the cover of the 'heel' of the battery cradle to expose the locking latch. Loosen the two screws and slide the latch approximately 1mm towards the toe end. Re-tighten the screws, replace the cover and re-install the battery. The point is to reduce the allowed movement of the battery.
The second problem (encountered after one year) was also a connection issue where the motor shut off for just a moment, but powered back on by itself with no error code. The assist level would revert from 'Eco' to 'Off', but I toggled back to Eco. And a hundred yards later had to do it again. The solution was to remove the control panel display unit, turn it around to examine the back and find a small Phillips head screw near the bottom of the back. Very gently, tighten that screw but don't over tighten. It feels like you can strip it out by barely tightening it. I don't know exactly what this screw adjusts, but it seems to affect the control unit contacts. I've had no more problems of any kind.
I haven't had any interaction with Shimano, except for having my dealer order an additional battery for me (mine is 504 Wh). Still waiting after 3 months for Shimano to get it to him.