I have the same version of LibreOffice installed. The problem is not only with exporting PDF to a network drive, but also with trying to "Save As" to the same drive. If I change the document and simply "Save" it, it works well.
I do not use the Libreoffice dialog box to access the network drive, I connect to it through Nautilus "Connect to server: davs://<>" etc. and then access it through Nautilus and open the document by double-clicking.
I have the same version of LibreOffice installed. The problem is not only with exporting PDF to a network drive, but also with trying to "Save As" to the same drive. If I change the document and simply "Save" it, it works well.
I do not use the Libreoffice dialog box to access the network drive, I connect to it through Nautilus "Connect to server: davs://<>" etc. and then access it through Nautilus and open the document by double-clicking.
I had similar problem once after distro upgrade, I believe this bug is related to it: /bugs.launchpad .net/ubuntu/ +source/ libreoffice/ +bug/1069757
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