Please be sure if using custom fonts to always test your watch face on an actual watch for they may not always work as expected. This may or may not actually be a Facer issue, but can be an issue just the same.
Working with fonts that are number only so that they are optimized to save space I have seen errors in some areas of the display that the numbers do not come in properly when uploaded to a watch, but looked perfect on Facer Creator. When replaced with the same exact font that was not optimized in this way, it fixed all the issues.
On some other watch faces using the full custom fonts, everything looked great in Facer Creator. But when uploaded to a watch, some areas looked just fine and others did not look proper. For these instances I just replaced the font with a stock font on areas that weren’t working properly. Everything then worked fine in these specific cases.
While it is always best practice to test all your designs on a real watch, not everybody has one to test with. In these cases you can always ask others in the forum to assist in testing it for you.
Hopefully my experiences and solutions are helpful.