Do you know if the "packet loss" counter at the bottom said anything during the time of the issues?
Also, if I'm reading the info correctly on your screenshot (I don't use this speed test much), but the current test you show has a higher than usual ping & jitter range (pings going from 28 to 537 and hitting over 3110ms on the upload, and jitter values between 73-100..). Some wild swings there, so I might see this connection as being unstable. Are you running all of your devices from some sort of 5g wifi tower type of device, which provides an internet connection through 5g or some sort of wireless cell service?
I am sure that packet loss was 0.0% every time which I used the test.
It's a fiber connection that has pretty good speed and is economical too but I don't have any idea about the high ping factor but it used to be in this way.