We have an entire appendix devoted to
test taking skills in both of our books. Since all questions cost the same, you can definitely skip harder/longer questions to finish shorter ones... But it depends how much time you've already spent reading it.
For example, if you spend 60 seconds reading a question only to discover it is a hard one, you're better off finishing it then coming back to it later where you might have to spend another 60 seconds remembering what it was about. Usually if it's hard, I eliminate 1-2 choices, make my best guess at an answer, then mark it to come back to later.
Remember, you have less than 2 minutes per question total, so every second counts! While some questions will certainly be easier, others will not.
I haven't personally encountered any bugs with the software, although I did have the power go out at my test taking center for a few minutes! Luckily, everything was saved and I picked up right where I left off. Did take 10 minutes to reboot the computers though.