Some things to try to see if the problem can be narrowed down or resolved:
a. Try resetting the network stack and check if that resolves the problem.
In the search box on the taskbar (click Start), type command prompt, right-click the command prompt result and then select Run as administrator and confirm.
In the Command window type the following commands one at a time and press Enter after each command and wait for a response before entering the next command. Yes there is a space between the words and the / character but not between the / character and the next word. If you make a typing error use the backspace key and retype the word or letter etc. Some of the commands may take a little while for a response and do not restart the laptop until all the commands have been entered (even if a response says to do it)
Type ipconfig /release and press Enter key.
Type ipconfig /flushdns and press Enter key.
Type ipconfig /renew and press Enter key.
Type netsh int ip reset and press Enter key.
Type netsh winsock reset and press Enter key.
Close the Command window and restart the laptop in the normal manner and check if the problem is still there.
b. Try using the laptop in safe mode with networking and check if the connection remains stable. If it does it may be a driver problem (but you have checked the drivers) or a 3rd party program may be causing the problem. Check what programs are loaded when starting the laptop. In normal mode right click on the Taskbar and select Task manager > Startup to view what programs are being loaded when starting the laptop and check if they are necessary or not. Some may be for correct operation so be careful. Check online what the program is for if you’re not sure. If you think that it may be a problem, right click on a program in Startup and select “disable’ and then restart the laptop and check the WiFi. If still no good right click on the program again in Startup and select enable to restore it again etc
c. Try using the laptop as close as possible to the router to check if the connection is stable. If so it may be an antenna problem in the laptop. If it works OK right next to the router, here’s the maintenance and service guide for the laptop taken from this webpage Go to p.39 to view the necessary pre-requisite steps and then the procedure to remove the WLAN card. You don’t have to remove the card but the procedure will give good access so that the antenna cables’ connection to the card can be seen. (see p.40 to view antenna cables on the card)
d. Try installing a free WiFi sniffer program to check the receive signal levels of the WiFi connection. The signal level is displayed in -ve dBm so the higher the number the weaker the actual signal is. A signal level of -60dBm is considered Good, -70dBm is Fair and -80dBm is Poor or is unstable
Also check how “crowded” the WiFi channel is that you’re using between the router and the laptop i.e check how many other networks in the vicinity are on the same channel and what their signal strength is. It may be that if they’re on the same channel and have a strong signal it could be interfering with the signal reception/transmission in your network. Most routers default to CH1, 6 or 11 straight out of the box so try using a “quieter” channel i.e. one with little or no appearances in the sniffer program, to minimize any possible interference problems. Check your router’s user manual how to change the WiFi channel number.
Apologies for the long answer but sometimes you have to eliminate things to find out what is happening.