According to the rules for Spell Scrolls, casting from a scroll requires no material components other than the scroll itself; similarly the rules in Xanathar's Guide for scribing a spell scroll say that you must provide the material components at the time of creation.
Well and good. But there are a few spells that have an unusual relationship with their material components. For example:
- plane shift requires a tuning fork specific to the target plane
- banishment requires an item the target hates
- Drawmij's instant summons enchants the sapphire component so that crushing it can summon the item.
- Leomund's secret chest requires a chest and its replica, one of which is sent to the ethereal plane, and the other is used to recall it or send it away again.
- contingency is all kinds of problematic in this context; if you ever don't have the component on your person, the spell instantly ends. (I'm not even touching the question of whether the writer or the user has to cast the contingent spell!)
How do those (and other spells) function when written into a Spell Scroll?
I can guess that a plane shift scroll might be inherently linked to a single target plane per the tuning fork used at the time of writing, so you don't really have a scroll of plane shift as much as a scroll of plane shift to the elemental plane of air (or some such thing), and a banishment scroll might only work on a particular class of creatures based on the item used in its creation; but in the other cases, the components aren't destroyed by the process of creating the scroll, so it seems like you'd need to have the scroll and the component(s) used in its creation in order to use the scroll, which is rather contrary to the whole concept of spell scrolls not requiring components.
Is it just up to the DM to figure something out? Should the special components vanish during spell creation and magically appear when you use the scroll? Or should these sort of spells just never be scribed onto scrolls, for the sake of everyone's sanity?
