In this trade, a lot of orgs put a lot of emphasis on "sprints" and "deliverables", but you really have to look at software development as a continuum. Optimizations and bug fixes are a part of this continuum, and any good team has space for these things in planning.
Not all teams recognize this, however, and I would recommend discussing with the other engineers on your team how you can work together to advocate for this. No sprint can be 100% features. Software requires upkeep. Bugs are a natural part of this.