I don't think it's a FileZilla bug because OP had the same issue with ftp cli from linux laptop. If anything it might be an compatibility issue with ftp and Humax. Having said that OP network is a little bit off because he mentioned resorting to mobile phone because browser access to WebIF wasn't working from laptop to Humax. Eg It might be something like MTU difference between devices, but that wouldn't explain why this is a recent problem.
I use Linux Mint 19.3. I have no issues. I can access my Humax fine using either cli FTP or FileZilla for transfers. My HDR has over 70 files and 50 directories in My Video. (The directories have further sub directories up to 5 deep and there are hundreds of files, but I don't think this bit is relevant.) I think the issue is with ftp timing out when trying to show/access just the My Video directory for the OP.
So I am the OP author
I can confirm that I now have FTP access to My Video folder, having cut and paste everything into my music using WebIF through opera browser on my phone over home wifi (because i can't access WebIF with any other browser/device combo!
I did mention using my phone data package to access WebIF at start of thread but I was mistaken I was connected to home wifi when getting access to WebIF on my phone
I can access all directories and their contents nested sub folders and everything using the webIF but when i use Filezilla the connection times out waiting for listings in any folder with i'd say more than 15 or so files. I haven't tested the exact number yet that is causing a timeout
I can access all folders and their contents using tnftp from within telnet session although it is quite slow to return listing
So i'd say this is narrowed down to something to do with Filezilla 3.50.0 on both OSX10.14.6 and linux ubuntu budgie or else something to do with filezilla and my home network! or filezilla and humax box since update of filezilla
i downloaded another ftp client on mac called 'commander one' and having same issue getting it do do a directory listing !
so maybe it is FTP and humax issue or ftp and humax on my network issue?
I'd say the issue started after i updated filezilla .
Any other input great appreciated
For now I am going just leave the 'offending' folders in My Music folder which I don;t use, so i can access My Video over FTP
I have just created a new folder "newmovies" uploaded 3 files each around 2.5gb and I can't get access to My Video again using filezilla. When I cut this folder and place it in My Music I get access via ftp back into my video again...aghhhhhhhh