Opening a story now starts the transition before the article finishes rendering. This should help with the delay, though I haven’t reproduced your intermittent multi-second pause. A recording would still be useful if it continues.
As you can see above I’m still waiting for v15.0.4 so maybe that will fix it, but I figured out how to reproduce the particularly slow load with the ‘Loading’ notification: force stop the app, reopen it and then it will happen for whatever story you open first:
Let me know if that gives you enough info to reproduce yourself; if not, I can share my app & system logs.