I htink this is a battery issue. I’ve been trying to figure it out, but it seems like this can happen pretty normally. In fact, Google recently sent out an alert about their similar batteries here: https://support.google.com/chrome/a/answer/9139543
Do not let the Chromebook battery fully discharge over the summer. Even when a Chromebook is off, its battery continues to slowly lose charge. If left long enough, the batteries might no longer function and can’t be recharged.
At the same time, you shouldn’t keep Chromebooks plugged into a cart or charger while in storage for months. This can reduce battery life and lead to other issues. If you’re storing Chromebooks for a long time, charge them to at least 80% and unplug them from a battery source, following the instructions below.