This is a workaround. It will check all visual differences. Open both Illustrator files that you want to compare. In each file, draw a rectangle with a stroke and no fill the same size as the artboard. Optional, but for convenience, group everything within each file. In one file, change everything to Difference blend mode in the Transparency panel. Copy all of the items from the file with the Difference blend mode objects and paste them into the other file. Line up both groups so that they are the same position on the artboard. That's where having a rectangle the same size as the artboard comes in handy. Any areas that are the same will turn black. You can quickly spot any areas that are different because they won't turn black.
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