Hi I've been using Sibelius for years and really feel that the arpeggio line system should be fixed by now.
I don't use the ones with arrowheads - they are seldom seen in proper scores.
When I highlight a chord to arpeggiate, I click on 'L' for line and select the arpeggio, a tiny dot appears that I have to drag up or down and it never wants to stay where you want it. They also seldom play correctly.
The arpeggio lines seem to be tied to voice1/voice2 etc and I wonder if that's part of the issue?
Why don't you use the Arpeggio lines options in the fifth Keypad layout? They function in a much more streamlined and efficient way, since they are effectively treated as articulations. Arpeggio lines created this way automatically have the correct length and keep their horizontal alignment with the chord even when specific note positions shift within it. They also playback well. One can use Sibelius for years and still miss a workflow option like this, as it seems you have!
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A composer www.markisaacs.com www.facebook.com/markisaacsmusic Sibelius 6.2.0 build 88, Bob Zawalich plugins, Windows 10 64-bit, Intel Core i5 7400 Quad Core Processor (3GHz-3.5GHz 6MB), 8GB RAM, 27'' monitor, NotePerformer 3.3.2, Sibelius Sounds, Sibelius Sounds Essentials, Sibelius Gold (Kontakt), Garritan Personal Orchestra 3, Garritan Authorised Steinway, Bose Computer Music Monitor speakers, Focusrite Scarlett Solo Gen 3.
Note, though that in all cases arpeggio lines/properties only playback in a single staff, even though you can drag them to another staff. You can use the installable plugin Harp Arpeggios to playback notes in multiple staves. That mechanism has limitations, but is the best tool currently available for playback across staves.