Because of my current advanced training to become a project manager I have to do a lot of research. Many of the sites I find I clip into Joplin and additionally create a PDF file out of the site. This PDF I attach to the created note.
My Joplin for Windows desktop has no problems with it and the PDF is visible inside the note in the PDF viewer.
But on my android smartphone I can't even download the PDF file. Nothing happens.
Therefore I searched this forum and found the following topic:
I just changed the configuration for attachments to manual but I could only tip on the link and nothing happened except the CSS defined reaction to the "click".
As suggested I moved the sync to Dropbox and it was to no avail.
First it took more than a day until the sync was completed and after I added new notes at my notebook with Joplin for Windows, they wouldn't be synchronized at the other devices.
Furthermore, because of my German heritage and language I prefer tags with mixed upper and lower case letters. Therefore I always change the stupid lower case words in the SQLite database with the help of a fitting editor into how I want them to be. But in the synchronized data of my tablet and smartphone some of them are like they should be (and were before) and others are all lower case.
Looking back a few months there were no such trouble.
Ok, how about reinstalling the app and syncing it from the scratch with Dropbox?
Please note Joplin does not have a background sync on mobile devices. When Joplin is closed, sent to the background or the device is put into sleep (display off), the sync is interrupted. So please disable the lock and leave it for several hours with the app in the foreground.
Also, don't forget about keeping the backup fresh.
I have no experience with problems you have, but don’t you want to try Joplin Server? It’s the best syncing option by far, so it may provide a solution for this. Just my 2 cents.