Can you try:
sudo modprobe -rv rtl8723be
sudo modprobe -v rtl8723be ant_sel=2
echo "options rtl8723be ant_sel=2" | sudo tee /etc/modprobe.d/50-rtl8723be.conf
Reboot, test.
If the above does not work, try switching to antenna 1:
sudo modprobe -v rtl8723be ant_sel=1
echo "options rtl8723be ant_sel=1" | sudo tee /etc/modprobe.d/50-rtl8723be.conf
Reboot, test.