I'm now using modded firmware v1.30 ("MOD4") from
https://www.goprawn.com/forum/ambarella-cams/11876-sjcam-sj8-pro-modx-custom-firmware/page3
I don't see anything about v1.30 on sjcam's web site or forum. The camera shows the firmware date as 2018-12-28.
I notice that there is now a "power on record" feature in the wand menu within Video mode (but it does not show up under Car Mode) and enabling it does work while in battery mode. I'm not sure if the old firmware had this since I was mostly using Car Mode. While in Car Mode and using battery only, turning on the camera still does not auto record.
I tested with 2560x1440 60fps HEVC (video quality=fine, gyro stabilization=off, distortion correction=on) and it still has audio problems and doesn't actually feel smooth like 60 fps (compared to GoPro 6). Also after about 16.5 minutes of recording and charging while stationary in the house at 65 F, the camera stopped recording with the "slow SD card" message (using Samsung Select 256 GB); the camera also crashed/froze soon after I changed the mode to Car Mode. Because of the crash or "slow card", the last file recorded was corrupt and could not be played.
After the crash, the camera's date and time reset back to 2018-12-28 00:00. All my other settings were still saved.
I then tested with 2560x1440 30fps HEVC (video quality=fine, gyro stabilization=on, distortion correction=on) and recorded for 28:32 and did not have any problems.
I'll probably stick to using 4k 30fps HEVC again.