"Jan 2015 – present" isn't misleading in itself as a way of specifying the period of time over which you have been volunteering.
It's only misleading if you present it as if it was a single, uninterrupted period, since it clearly wasn't uninterrupted.
If you have the space, you might consider something like this:
Jan 2015 – present, various short-term volunteer positions at Acme Club
- Jan 2015 – Aug 2015, role 1
- Dec 2016 – Jan 2017, role 2
- Dec 2018 – present, role 3
For positions where the details aren't relevant, you can just cut out the bullet point list entirely, leaving just the heading. Since it's specified "various short-term volunteer positions" (or something similar), I doubt many would interpret it as a single, long, uninterrupted period.
For positions where the details are relevant, listing the different roles separately under a heading provides the benefits of both easy readability and the required details.
Notice how this isn't really all that different from how you might present a long-term job in which you showed a progression in skills and assignments.
Also, unless the place where you volunteered is really well known, then you probably want to add a very brief (one or two sentences tops) summary of what they do, and maybe a web site address where one can learn more. Presumably there's a reason why you're including it on your CV in the first place; help the person reviewing your CV see that reason.
And remember: you don't really have one single CV. Rather, think of the document you work on as your master CV, which you tailor to each job application. It's far easier to cut things out when tailoring than to add things.