HI,
The unit in “custom format” for # in the attribute settings did not have a spacing as default.
Not sure if this is intended. 
Hi @ch.lau 
Welcome to the community, we are stoked to have you here 
You are correct, this is a small issue, you can add the spacing manually but it disappears on its own after you refresh or visit your board again!
I’ll make sure to increase the importance of an already existing ticket for this. It does have a very small priority - as it does not affect your workflow or disrupts you from working at all (it’s more of a visual issue than anything else) - but it should be fixed at some point! 
Thank you for reporting this to us! 
Cheers 