Overheating and excessive battery drain by application - Facebook App.

Facebook is not an Apple product. Contact the app developer here --> App Support or Facebook Help Center | Facebook

For overheating issue --> Overheating issues with my iPhone - Actio… - Apple Community

For Battery Drain --> Prolong and Maximise Battery Performance … - Apple Community

"Overheating and excessive battery drain by application - Facebook App.: [...]so far iPhone is not over heating and I will charge to 95% and watch over next 14hrs to see if this issue is resolved. Unsure if anyone else is experiencing same issues. My cellphone is not in direct sunlight or being used differently than pre upgrade...noted same to support."

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Troubleshooting an Overheating Phone:

Clear Space, as system resources may have been swollen up. Clearing caches (by deleting System Data), you may fix an app causing this.

Troubleshooting iPhone Storage:

Internal storage cannot be upgraded. It is what it is. So, the maximum internal storage capacity never increases, even if you upgraded your iCloud plan. Learn More here: What's the Difference Between Device Storage and iCloud Storage? Apple Support

So, what to do...

Clear Space Using my User Tips:

• How to Clear Space from your Mobile Device, and What to Clear: - User Tip. You may have too much installed, and need to clear space. So, see my user tip: 
• How to Clear "System Data" in your iPhone's Storage: - User Tip Caches would be being used for remembrance of application use. You'd backup your iPhone, and then restore your iPhone from the backup you've just created. All System Data will delete.