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Probably more of an oversight of today's change that made it left-click activate instead of left-click equip. If you change its setting does it allow you to bank it again? Also could be a side effect of the new setting and not something easy to work around.
Tagging /u/jagex_stu as IIRC they were the ones that worked on this (all the recent QOL changes are blurring together but I know Stu had his hand in a few of them so sorry if this wasn't you, Stu)
It's a consequence of you now being able to dynamically flip Excalibur's first two options specifically in the backpack, worn equipment and action bar. The bank replaces "Remove" with "Remove to bank" and won't find it in this case because it's now "Activate" from the bank's perspective.
Thanks for confirming my suspicions. :)
Also to confirm for OP - swapping modes doesn't bring back the old behavior (just tested).
I've just implemented a fix to force those "Remove to bank", "Remove to inventory" options onto all the Excaliburs in the bank's worn equipment panel.
Release'll probably roll to January's community hitlist, as we have limited update slots for the remainder of the year, and it can be worked around.
Thanks for raising the issue!