Extremely simple to find out.
Run a test via ethernet, if OK here then you know issue with WIFI.
WIFI is susceptible, you probably already know this am just beating a dead horse, to neighbor's interference, appliances, wireless speakers, wireless handsets. You have a WIFI applet that tells you signal strength as well as (tell-tale sign of interference) Signal-to-Noise. A large SN, clean signal, a low SN, lots of interference.