Sure! One of the big things we’re reworking for 2.0 is how we handle accounts, which includes changing the format of how we persist account information. The compatibility changes in this build add extra decoding logic to the account persistence system so that both v1 and v2 can load a saved account regardless of which version saved it.
TL;DR: Mlem v1 is not fast; Mlem 2.0 (announcements coming soon!) will be.
We’re aware of a number of performance issues with the current codebase, which all together result in the app not behaving as responsively as we’d like. Unfortunately these are largely due to design choices made during the hectic sprint to App Store release last summer, and so are infeasible to fix without rewriting the app from the ground up—which is why that’s precisely what we’re doing. Our 2.0 build should be significantly faster; we’ll have some announcements about that in the near future.