'space' not fixed width in mono space font?

Hello,

I want characters to line up vertically so I use mono space fonts like Roboto mono and others.
However it seems that tft_espi prints a 'space' smaller then the fixed character width.
I.e. two strings printed like this;
1234567890
1234 67890
.. the space will take less room thereby shifting the remaining chars to the left.
Any ideas what is going wrong?

Thank you.