My experience with WiFi problems it is mainly about:
- Linux Headers
- Drivers
Try to install “linux-lts-headers” and “broadcom-wl” or “broadcom-wl-dkms”
I am not sure about your hardware or your installation, but the best is to go with defaults which uses LTS Kernel.
You may check Internet connection is way too slow - #6 by limotux
I hope this helps.
Please let me know if this is of any help.
Thank you.