I've read other posts about the same issue (very few posts, though).
Try this, if not already:
Exit Camera app
(phone) Settings > Apps > Camera
Force Stop, lower right
Storage, Clear Cache
Storage, Clear Data
... and now:
Press and hold Side key until you see Power Off - select it to power off the phone.
Now, off to the Maintenance (Recovery) screen:
Press and HOLD the Volume Up key, and while holding, press and HOLD the Side key.
When the Samsung splash screen appears, release both keys. Within a few seconds, you'll see the Maintenance screen, with a number of menu options.
Use the Volume Down key to highlight Wipe Cache Partition. Press Side key, select "Yes".
Now, Use Volume key to highlight "Repair Apps" (should be last menu option). Use Side key to select it.
The phone will automagically restart. Let the phone settle down for a couple of minutes.
... retry Camera
Take pic even after subject immediately moves and play it back in gallery and find the perfect shot, then save with little capture icon bottom left.
Hello @Firemancliff ,
Thank you for your feedback. If you haven’t already, Please update Samsung members app to latest version from galaxy store and send us an error report immediately after experiencing the issue from the Samsung member’s app -> Beta Feedback -> Error Reports to help us debug the issue. We apologize for the inconvenience and appreciate your contribution to the beta program.
Please try experimenting with motion photo or pet mode or a burst shot when taking kids pictures.
One UI Beta Team