Microsoft Azure DNS extension is used to synchronize DNS zones to Microsoft Azure DNS.
TXT records with the same host are concatenated.
The "SPF Record Lookup" on mxtoolbox.com shows the following result for "SPF Syntax Check" test:
CONFIG_TEXT: "Invalid syntax found"
Microsoft Azure DNS extension bug with ID EXTPLESK-1319.
As a workaround, manually update the concatenated TXT records on Azure DNS side.