In ArcGIS Pro, labels containing the letters ‘f’ and ‘l’ together with certain font types, and Spread letters is enabled, do not respect the letter spacing.
The fonts referenced in this bug support ligatures. If ligatures is turned off, the label displays as expected. To turn off ligatures, on the label class pane:
Click the Symbol tab > Formatting tab > un-check Ligatures in the Formatting group.
解决办法
Use ‘F’ and ‘L’ or a combination of upper and lower case letters.ORUse another font except the ones mentioned above.ORAdd <FNT size="1"> </FNT> between 'f' and 'l'. For example "f<FNT size="1"> </FNT>lorida".