Fixing Synology DS413 slow transfer speeds

I have an ageing Synology Disk Station 412 NAS. It used to be capable of very reasonable 100MB/s transfer speed. At some point, I enabled share encryption, which reduced transfer speeds by about half. It was chugging along like this for quite some time but then noticed that speeds got even slower. After a quick test, I found that upload to an encrypted share was lingering at around 10MB/s, downloads were maybe double of that.

Synology NAS Let's Encrypt Certificate error: "The Operation Failed"

Issue

Trying to add Let's Encrypt certificate on Synology DS918+. The process fails with error:

The operation failed. Please log in to DSM again and retry.

There are no obvious reasons for the error. Port 80 is open, Synology Log Center doesn't have any clues.

Batch delete multiple videos in YouTube Studio

Currently (as of June 2019), there is no option in the new YouTube Studio (still in Beta) to batch delete multiple videos at once. You have to click the Options button (three vertical dots) next to each video and select Delete.

HP Officejet Pro 8600 Plus - no longer scans to SMB shares

Issue

HP Officejet Pro 8600 Plus refuses to scan to a SMB share on Synology DiskStation NAS.

When trying to scan, device's LCD screen displays following error:

Connection Error
Cannot connect to \\192.168.0.15\scans. Make sure the remote computer is turned on.

Printer's web GUI shows following error when testing Network Folder connection (Scan > Network Folder Setup > Test):

Connection failed...