So many internet provider have adjusted their delivery services so that systems slow down at certain times... you might keep some tabs on when it is slow, then see if it is faster at a variety of other times. The bad times for us, county wide, are between 7a and 9a, 1p to 2p, 5:30p to 7:30p... and almost any time on Saturday. But I understand it varies from one locale to another.
Also, some connections at 1.5 gpbs and 4 gbps were a lot faster than advertised. Now the providers have systems that automatically gear down the connection speeds to a bit below what you are paying for. If you don't complain, they keep on doing it.
Using Speedtest will verify when and if it is slow,