If you have FTTP , then there is no training period like rate adaptive systems that vary speed depending on line conditions, you get the connection speed you pay for , provided the correct profile has been applied to your account , and with optical systems the light level is key, sufficient power means you connect, insufficient and you get LOS ( loss of signal ) and it doesn’t work….its not the case that if the level is low speed is reduced accordingly, it either works or it doesn’t, have you noticed if the red LOS light has been lit ?
There have been many posts on this and similar forums , complaining that the speed the customer is getting is less that they expected, but in every case I recall , the problem was with the customers kit , being incapable of using the speed offered ( 100Mb Ethernet controller for example is going to limit speed to that rate ) , WiFi , unless using cutting edge gear, is not going to perform anywhere near wired connections speeds, it’s possible there is a fault at the headend , but you would expect every member in the PON to be affected , not just you.
Your issue does seem strange as your recorded speeds vary massively…it needs to be accepted though that you do not have an exclusive connection, you share your PON with upto 32 others , although policy seems to be a max of 30….you and these others share a download bandwidth of 2.4Gb, if you happen to be running a speed test when these other customers are consuming large amounts of bandwidth then obviously the throughput ( not connection speed ) will be affected ….try running a speed test when it should be a quiet time ( say after midnight ) …also , if you have family members online at the time you do a speed test then obviously they are going to affect the speed test result, you need to test when no one and nothing else is connected to the router.
