Is this the latest version 9.1?
Please always specify the version when you submit a question or bug. Otherwise I can't really help in a deterministic way.
I can only dig in the latest version, otherwise I could be spending hours to try to replicate a bug that may not exist anymore.
Anyway, in the graph export there is a 100k hard limit, look in gateway.js for "100000". The screen graph will never load that many data points.
If you want to export ALL data of a node (between some certain dates) then use the Download All Data button on the Node dashboard.
There is a parameter in the Download All Data (CSV) dialog called "Max points/metric:". That is defaulted to 10k points but you can increase it to whatever.
Notice the timestamps you see differ only by hour.
(This means) Timestamps are in GMT, you will have to adjust to your locale. A future improvement would be to add a dropbox to choose to adjust the timestamps to a specific locale. You could
open a issue at Github for this improvement.