Black frame at the end of animated gif after rendering in PE 2021

1. Created a 10 sec video loop 5sec + 5 sec of reversed timeline

2. Renders fine into a .mp4 clip from .prel file

3. But rendering into .gif creates a black frame at the end of gif, and will not loop

(also rendering of  a .gif file is slow, low quality with a choppy progress)

What is the issue?

N.B. Importing a previously rendered .mp4 clip and then creating a gif works fine

Thanks, Adam