In a move reminiscent of Apple infamous "Error 53" problem, where the update to iOS 9.2.1 caused iPhones that had been repaired stopped working, it seems that iPhones that have a had a non-Apple display replacement are being rendered useless. The issue seems to be limited to the recently released iPhone 8 where the display has been replaced by a third-party and then upgraded to iOS 11.3.
As was the case with Error 53, Apple is taking their time to recognise that this is a problem.
The original issue, which was reported by Motherboard, has led to repairers either having to recall thousands of devices or simply refuse to fix new hardware until issues like this are identified and rectified.
If this issue affects Australian iPhone owners, you can expect the ACCC to get very interested. Last year, the regulator launched legal proceedings, alleging that the Error 53 issue was a contravention of Australian competition law saying "The ACCC would also be concerned about any practices which restrict competition, including through access to parts or data”.
If you've broken your iPhone's display then your safest bet for a repair is to go to Apple for a fix. If you've paid for AppleCare+, the costs are a reasonable $45 but jump markedly if you haven't sprung for that insurance/extended support.