I've got this issue starting about a month ago in the iOS Garmin Connect app. The issue is still there in the latest version of the app 4.59.0.30
In the Edit Exercise screen, when I tap a Weight field and tap the next Weight field, the keyboard just disappears until I tap the Weight field again. This also happens when I tap the next/previous arrow on the keyboard.
This makes entering the same weights for an exercise a tedious process.
This issue wasn't there before. I used to be able quickly tap the Weight fields and enter the value without the keyboard disappears each time.
Here's the video of the issue