Multiple cycles of simultaneous GATT connects and disconnects to multiple nearby peripherals make the app fail to connect, after a while. This affects all apps (i.e., it has nothing to do with the app). Once the device is in this state, no app can connect to any Bluetooth LE peripheral.

I wrote a small app based on the BluetoothLeGatt Google sample code that demonstrates this issue. The demo app scans for nearby Bluetooth LE peripherals and shows them in a list while connecting to them. After a connection to a peripheral is made, it removes the peripheral from the list and starts the cycle over.

Android build
7.0 NRD90M.G925TUVS6FRC1
7.1.1 NMF26X.J510FNXXU2BRE6

Steps to reproduce
1. Download and run the demo app: https://github.com/zssz/BluetoothLeGatt
2. Upon first run allow access to the device's coarse location for scanning for peripherals to work. Restart scanning in the top right corner.
3. Make sure there are Bluetooth LE peripherals in range. Note: the more, the better, because the issue will appear sooner. In my case with 7 peripherals the issue appears under 3 minutes.
4. Leave the app running.

Expected result
Until the app is stopped, you can see peripherals appearing in the list and shortly after disappearing.

Actual result
After a while, depending on the number of nearby peripherals, you can see that the list doesn't change anymore. This means that all of the peripherals are in the connecting state, but won't connect.

Frequency
100%

Video recording
https://youtu.be/AnbkHN7suPE

Fix
Restarting the app doesn't fix the issue. Neither toggling Bluetooth in Settings. I found 3 ways of fixing it — all of them require user intervention, unfortunately:
a) Go to Settings / Apps / ... / Show system apps / Bluetooth / Storage / CLEAR DATA
b) Go to Settings / Apps / ... / Show system apps / Bluetooth / FORCE STOP
c) Reboot the device