Your issue sounds more like it relates to end-user bandwidths not being what they used to be.
If you've changed nothing about the content files for these courses then the only other reason why things are not working must be due to some change in the IT environment.
Slow loading times suggests bandwidth has come under pressure for some reason. You need to start doing some tests to find out what the ACTUAL bandwidth is at the end-user where these issues are being reported. If they all have good bandwidth, then you need to look more at the load being placed on your server. Perhaps a lot of other content is also being served now (e.g. video content) and that has choked the server's outgoing bandwidth.