Try using an alternate method of using Playlet and see what happens.
You can use Playlet through a web browser on a laptop, or use it on a mobile phone (using the Youtube app).
Try the mobile phone method. (The instructions are under "Remote", directly under the Settings in Playlet).
1. Install Youtube app on phone/mobile device.
2. Go to the Remote section in Playlet and select "Link with Wifi" (use the arrow keys).
3. In the Youtube app, search for a video and then press the Cast button on your phone and select "Playlet on Roku Device".
4. Then press Play on the video in the Youtube app.
Your Youtube video will now be sent through to Playlet.
The other method is to use a web-browser on laptop (Select Playlet Web App) and follow the instructions there.
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See if you have any better results using one of those two methods.
I prefer using the laptop (Playlet Web App) but use whichever one is easier for you.