It is not impossible that there may be a node or three missing in the OSM route which maybe causing a glitch in the calculation.
Try the following:
1- Ensure your version of BC is the latest one
2-Manually create a series of waypoints in BC
3- Create a new route in BC by drag and dropping your points in the routing window and see what transpires.

You may want to check the settings in the Motorcycling profile in BC to make sure these match those in your gps.
Shortest, fastest, avoidances etc etc
Soooo many settings!

When BC is running ( or anything other program for that matter, you can take a screen shot of what you see- 2 options - one where you use a rectangle to select an area you wish your image to be or one which takes the whole screen.
Opening (in windows) the resulting image ( Open with option) the little program called 'Paint' enables you to add arrows/lines/text etc etc to your screen shot.
Then you chose ' Go Advanced' and chose 'Manage Attachments'
Select each image then press upload when replying on the Hubb to add images to upload.
Tip - resizing your screenshot image to 800 X 600 size reduces upload time and clutter on HU!

Why anyone would want to 'iron butt' around Ireland is beyond me! There are so so many simply fabulous places to eat, drink and be merry there! Durty Nellys to mention but one!
Ahhhh fond memories of the Emerald Isle and its fun loving people. (except that little turnip who insisted I leave the pub at 04:30 really.... !! )

Durty Nellys is here 52.696387,-8.811943