Just to be clear, the applets were stuck while the laptop was plugged in? If so, then it might just be the threshold - connected, not charging, not discharging (because the laptop is running off the AC adapter).
For example on my IdeaPad laptop, when I enable the charge limiting feature it will get “stuck” at 59 or 60% while plugged in. It doesn’t have a configurable threshold. Although your laptop might provide a more fine-grained control given that you were able to fully discharge it while plugged in.
Maybe you’ve tried that already, but does the tablet show up as a USB device when you connect it to a computer? Android devices tend to enter fastboot or another firmware upload mode when everything else fails.