JUncaught Error: Font bitmap must be a String, in lato.app.jss

I wouldn't worry about MEMORY_BUSY, it's just a warning and is unlikely to affect the code.

I think what's been hit is something I noticed with the slopeclock as well.

Basically when you have a custom font, you've got the code in something like setFontLatoSmall which does this.setFontCustom(E.toString(require('heatshrink').decompress(atob('...

The issue is that E.toString is used here to create a string from the array, but it has a second effect - it tries to force what is has into a 'flat string' and if it can't it returns 0. Over time the memory can get fragmented and then sometimes it gets so fragmented there's no way to allocate a contiguous memory area of the length needed, and 'E.toString' returns undefined and this breaks.

It's a tricky one to fix nicely, since I can't change E.toString to add an option like {forceFlat:false}as it's supposed to use all it arguments. I could add E.asString or something like that and then we change all the font code to this.setFontCustom((E.asString||E.toString)(require('heatshrink').decompress(atob('...?

I guess the nice solution would be to rename E.toString to E.toFlatString, and to make E.toString just use a string if a flat one can't be allocated - but that would make anyone's code that uses Inline C/assembly unstable unless they changed it.

The way to work around it in your clock is to pre-allocate the font bitmap as was done here: https://github.com/espruino/BangleApps/commit/c47bc078acf593e3e7554c557c1fa01fd68fc14a

The side-effect is your clock actually works a bit faster too, at the expense of more RAM usage.