I've been having similar issues with international for the last week. Late afternoon and evenings the speed drops significantly. I have been doing speed tests to London and I get less than 10Mbps. Did 2 test now and they were 2.5 and 3.2 respectively.
It does get a bit better during late evenings, but it's only during morning and early afternoon where the speed is normal.
Local runs at expected speeds during the same time.