Like mentioned by @yuromastic, have you tried pausing or turning off the Video Data Saver? If the streaming service you are using can't auto adjust its definition for a lower speed and it's streaming in HD, the Video Data Saver can cause all kinds of buffering, as it's designed to throttle the speed of the service while streaming to save data.
So turning this off will help with buffering but use more data?
If the source is streaming in HD you'll almost assuredly use more data than with the Video Data Saver on. However, if the service is already streaming in SD and it's buffering because the service speed is just too low, chances are turning the VDS off isn't going to make a difference, nor will it use more data, at that time and with that streaming instance. It may later, though, if the speed of the service picks back up. That's why I tend to pause the VDS instead of turning it off, as it will turn itself back on in four hours when pausing.