One reason for significantly worsening fibroscan, despite taking NUCs for prolonged time, could be another liver disease, such as fatty liver or NASH.
This should be investigated IMO...
How is your liver enzymes?
I am on entecavir over 2 years. My liver enzymes are no improvement, Fibrosure result is worsened than last year, I had Fibroscan done once but no more, so could not compare.