Suggestion: Make the "repeat build" keyboard hotkey work the same as the UI button you click with your mouse.
Right now, they almost but not quite behave the same: If you select multiple factories, some with repeat build on and some off, the UI will show repeat build to be off for them.
If you click the repeat build UI button, repeat build will turn on for all of them.
If you press the repeat build hotkey for the same setup, repeat build will turn off for all of them.
Not only is this inconsistent (why should the behavior vary between mouse and keyboard?) but the UI button behavior is actually preferable:
If you select multiple factories, some with repeat build on, some off, the button will show repeat build to be off. As such, you can't be sure if repeat build is off for only some, or all of the factories selected.
For the UI button, this doesn't matter. In both cases (some or all off), pressing the UI button with the mouse will turn on repeat build for all of them. The behavior is predictable.
The problem is that the keyboard hotkey behavior is not predictable in this situation.
If all of them are off, pressing the keyboard hotkey will turn them all on.
If only some of them are off though, pressing the keyboard hotkey will turn them all off.
This is bad, because from just selecting the factories you couldn't have known their repeat build state a priori!
Interestingly, the "pause" button does work the same way for both the keyboard hotkey and the UI button, in both cases using the preferable behavior.
TL;DR: Make the "repeat build" keyboard hotkey work the same as the UI button because the current behavior is inconsistent between the two and the UI button's behavior is preferable.