The admonition still stands: Do not put your DEVONthink databases in any cloud-synced location or you could irreparably damage them. One instruction to follow and there’s no need to wonder or worry. Simple 
PS: We are not the only software developer stating you should not use Dropbox in this manner.
And we have stated numerous times you can use File > Database Archive to create a safe ZIP file for secondary backups.
Also, this should not be your primary backup. Get an external hard drive and Time Machine at a minimum for local backups.