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

I have been trying to catch a hang bug I see very rarely with my Lato clock.
I suspect that the problem is not down to Lato as the clock will run for days without issue
I was trying the mitherm app yesterday and that went offpiste and I had to reset the watch - so it might be associated with that. Prior to installling that app everything had been fine for 10 days or so. Theat could just be clutching at straws as I dont have a reproducable test case for this problem yet - its very random and rare.

Last night I woke up at 5Am and noticed the clock said it was 2:37am - ie the hang had occurred.

This morning I managed to retrieve the log.txt file and can see the following.

The question is, what caused the MEMORY_BUSY ? and did that corrupt the app code ?

 ____                 _ 
|  __|___ ___ ___ _ _|_|___ ___ 
|  __|_ -| . |  _| | | |   | . |
|____|___|  _|_| |___|_|_|_|___|
         |_| espruino.com
 2v16.93 (c) 2021 G.Williams

>
Interpreter error: [ 
  "MEMORY_BUSY"
 ]
New interpreter error: MEMORY_BUSY
>
-> Bluetooth
<- Terminal
>
Uncaught Error: Font bitmap must be a String
 at line 3 col 8328 in lato.app.js
...NDg0="),25+(scale<<8)+(1<<16));return this;
                                         ^
in function "setFontLatoSmall" called from line 3 col 8784 in lato.app.js
g.reset().setFontLatoSmall();g.setBgColor(options.bg).setCol...
                           ^
in function "draw" called from line 9 col 643 in clock_info
options.draw(itm,itm.get(),options);
                                  ^
in function "drawItem" called from line 9 col 2867 in clock_info
drawItem(menu[options.menuA].items[options.menuB]);
                                                 ^
in function "redraw" called from line 3 col 8602 in lato.app.js
...,h/2);clockInfoMenu.redraw();if(drawTimeout)clearTimeout(draw...
                               ^
in function "draw" called from line 3 col 8690 in lato.app.js
drawTimeout=undefined;draw();
                           ^
in function called from system
>
-> Bluetooth