The Pixel 5a apparently runs too hot. Google is investigating.

Google launched the Pixel 5a just a few weeks back and the mid-ranger is already creating problems for some of its users. Multiple reviewers and testers are reporting that the phone has overheating issues just like the Pixel 5 did when it launched. For many, the issue seems to crop up when recording 4K videos at 60fps. According to folks over at CNET, shooting videos in the higher frame rate causes the Pixel 5a to stop recording even in a normal environment. Reviewers at Android Police also had their Pixel 5a units throw up a warning message after just over five minutes of 4K recording.

https://www.androidauthority.com