I've never seen this issue, sorry. How do you check that the modelines have actually disappeared? Arcade OSD?
Yes, I check by Arcade OSD.
I have tried disable EDID emulation and re-install the driver 18.5.1 several times, but the problem remains.
Eventually, I solved the problem by the following tries:
1. Uninstall driver 18.5.1
2. Install driver 16.2.1
3. The modelines no longer disappear after restarting, everything works fine, except AMD pops up a error message box about improper driver
4. Then I uninstall driver 16.2.1, and install driver 18.5.1 again
5. This time, the modelines no longer disappear after restarting, and the AMD message box does not pop up anymore
Hope my experience might help someone in the future.