Install and test many of the most recent kernels. Test at least kernels 5.1, 5.2 & 5.3. Install kernels through Manjaro Settings Manager, and always have at least two kernels installed at all times for safety.
Disable MAC Address Randomization with the following command:
echo -e "[device]\nwifi.scan-rand-mac-address=no" | sudo tee /etc/NetworkManager/conf.d/disable-random-mac.conf
After creating the new conf file, reboot both your router and your computer.
Repeat this command up to 5 times after you have been disconnected to see if the network reconnects:
sudo modprobe -r mwifiex_pcie; sleep 3; sudo modprobe mwifiex_pcie
If there is no improvement, then run this command:
sudo systemctl stop NetworkManager; sudo ip link set wlp1s0 down; sudo modprobe -r mwifiex_pcie; sleep 3; sudo modprobe mwifiex_pcie; sudo ip link set wlp1s0 up; sudo systemctl start NetworkManager
You may want to repeat that command as well.
Please post any outputs of those commands.