The user created crop presets do not move the crop guides like the built in presets do, or like they did in 1.6.5. This is an issue that's been reported in a few other threads (see below) in releases after 1.6.5 to 1.8.0 betas. It was reported to be fixed in the 1.8.0 GM release, but it seems to be back.
https://forum.affinity.serif.com/index.php?/topic/81215-fixed-user-created-crop-tool-presets-have-no-effect-170258/
https://forum.affinity.serif.com/index.php?/topic/87288-the-user-created-crop-presets-dont-seem-to-work-properly/
https://forum.affinity.serif.com/index.php?/topic/96392-user-created-crop-tool-presets-have-no-effect-172471/
https://forum.affinity.serif.com/index.php?/topic/94979-crop-problem-still-not-fixed/