I had a similar experience today with my 2016 30kWh 8 capacity bar Leaf today. Temperature was about 50 F, so not cold at all. I started with 10 charge bars (about 14 kWh, according to LSP). Going 60 mph on the highway, slightly uphill but nothing crazy. The car started dropping charge bars very fast (one every 30 seconds or so) and it went into turtle mode. I slowed to 50 mph, and it came out of turtle mode but would slip back into turtle mode off and on. When I got off the highway and slowed even more, the charge bars started to increase. I plugged in to an L2 charger for an hour and it seemed to be working as normal.
I know I already qualify for the replacement battery under warranty. I was hoping to make it through the upcoming summer first because we have hot summers. My warranty period expires March 2024, so that is not a problem. However, if it keeps doing this, I will have to do it sooner. I just hope it is only the battery and not the BMS. I don't think the BMS is covered under the warranty.
Any comments or suggestions?