Connecting between letters issue

Hi, I want to create an Arabic font, but I also have this problem with the created font, the connection between the letters is visible, how can I fix them?
Screenshot:

Are the joins visible in the Font Test window at large font sizes?

No, there is no problem in the preview window at large font sizes, but there is a problem with the small size.
In fact, after changing the font size, the problem changes between the other letters!

The problem was solved by increasing the shape outwards of the metrics.

Good to hear you solved the problem!