Hmmmm, that does sound like a server glitch. I will run a few checks for you but they may be inconclusive if it's a sporadic fault. In which case you could always reset your hosting ( warning, resetting your hosting should be a last resort as it totally wipes all files and begins again from new. A backup of all files is needed and take screenshots of everything, just in case you need a visual aid to replicating stuff! Speak first with support if unsure of anything!). Resetting your hosting can fix problems like this if all else fails.
Your FTP port (21) is closed, so this would suggest your settings rather than a server issue. Try and find out why this port (21) is shut.
I think the problem is with your ftp settings on your site, rather than a server issue as port 21 (standard ftp port) is not open. So I would check your FTP settings.