Yep, It's very bothersome to be tangled inside the font issue.
Actually, I find out the cause.
My pharo folders with images and sandstone files are synced with cloud
(synology NAS) in order to allow update at my different work places.
I found that if I triggered image saving several times too quickly, the
updates get trouble inside what the image was saved, maybe the font files
were lost or conflicted as a result and error occured while reopen that
image.
I quitted the cloud synchronize and the errors resolved.
Best regards.