Inconsistent connection and super slow speed with RTL8723BE

Does your installed version of the driver have this parameter?

parm:           ant_sel:Set to 1 or 2 to force antenna number (default 0)

Check:

modinfo rtl8723be

If so, I suggest that you do, in a terminal:

sudo -i
echo "options rtl8723be ant_sel=2"  >  /etc/modprobe.d/rtl8723be.conf
exit

Reboot. Is there any improvement?