On the Reolink client software is “Overwrite” checked?
Device Settings – (Record) Option – Overwrite
My understanding of your post is that the internal SD is full and saving to the thumbdrive fails.
You might have found an issue to be aware of. I noticed that saving to my FTP server stopped at some point also. The internal SD card would have been full also. I did not look into possible causes or solutions and instead only use the internal storage now. Overwrite was checked in my setup. Hopefully someone here will know the answer.
Just want to add one more observation on my /var/log/vsftpd.log; whenever it gets full, I don’t see any FTP command DELETE send over to the FTP Server to request to remove the earliest video file before uploading the latest one.
So could this be the root cause of the problem that the REOLINK firmware did not issue the DEL command to the FTP Server before uploading to a FULL hard disk?