Developers wanted! No I'm not a recruitment agency

I'm relatively new to the field. Been working 2 years as a Web developer at the same company. So I want to ask, is it normal to be made to sprint plan live issues for any websites you maintain?

I don't really understand can you please explain more?

So I have a backlog in Jira with a whole bunch of existing bugs in production which I am being asked to provide estimates for and to plan a sprint with these estimates. Is it common practice to work on production issues in sprints? If so how do you estimate a bug without finding the cause of it which is most of the effort required to fix it?

Hopefully that made more sense. Very sleep deprived today!

You have to do it somewhere, might as well do it at sprint planning considering you need to either add it to the sprint or underplan your sprint so you have enough time to deal with production bugs.
As for estimation, I hate that part even in tasks, let alone bugs. Fortunately it's often recognised that those estimates are loose. Sometimes very loose. You usually think about what might be the issue and go from that or if you can't figure out what might be the issue agree on a default value that's not taken seriously.

I'd go with what @Bikonja said