I am looking at upgrading a large website that has been using phpBB 2.0.x for a number of years.
For a sense of scale; The website itself has been active for almost 20 years and as of right now has 1,133,682 posts and 13, 267 members.
I am not an administrator of the website, but am collecting data about what would be required to make a transition from phpBB 2.0.x to 3.2.x. I've read the support material regarding how such a transfer is done. However, I wanted to see if anyone here had advice regarding what to watch out for and what to expect when attempting to migrate large websites through versions of phpBB.
What should we watch out for and be aware of in looking at such a transition? Are there particular difficulties caused by trying to migrate a large website that a smaller website would not experience? Is there a risk that the transition could fail?