I was having these problem with rtl8723be on ubuntu 16.04.

I had to install new module for realtek wifi cards where they solved the constant disconnects:

install required packages

sudo apt-get install build-essential git
git clone new realtek wifi modules

git clone https://github.com/lwfinger/rtlwifi_new/
enter the directory

cd rtlwifi_new
build it

make
install

sudo make install

Now you can reboot or unload/load modules

unload modules

sudo modprobe -r rtl8723be

load new module

sudo modprobe rtl8723be

if it still doesn’t work, try the solution from this post

echo "options rtl8723be fwlps=0" | sudo tee /etc/modprobe.d/rtl8723be.conf

Note: After each kernel update, you need to rebuild the modules. That is,

After every kernel update:

cd rtlwifi_new

Clean previous builds

make clean

Update git repository

git pull

Compile

make clean && make

Install

sudo make install

reboot or unload/load modules