HMD has released the Google December Security patch globally for the Nokia 5. This update is 111.5 MB large and brings the software stability updates besides the standard security patch. On my Nokia 5 I also had a bug that prevented apps from staying in the RAM. After the update, the bug seems to be fixed since apps are not reloading when called from memory.
The updated came earlier for the Indian Nokia 5 models and now seems to be available globally. If you still didn’t update your device head to Options > System update and check for updates.
Tell us if the update is available, mention model number and if everything went OK.