Why does Dashlane use so many ports?
For those who are unaware, these &quot;ports&quot; in question are not network ports, they are Mach kernel ports and are used by the kernel for interprocess communication.  There is a fixed number of Mach ports that your system can have open, so to answer your third question; yes, this could cause problems for you as you approach that limit.  Given that the port count is so high, increases to as high at 90K or more, and that nothing else on the system is using anything close to that number of ports, I think it is safe to say that Dashlane is leaking Mach ports.
To answer your first question, I would say that this is unintentional behavior on the part of Dashlane.
And to answer your second question, I am not experiencing this issue; so some other people do not experience it.
Check out this great post on leaking Mach ports in Chrome for more geeky information:
https://robert.sesek.com/2012/1/debugging_mach_ports.html
What I would do in your case:

Uninstall Dashlane.  Also delete files from ~/Library/Applicaiton Support/Dashlane
Reinstall Dashlane using the installer on their website
Watch to see if the problem returns, and if it does, contact Dashlane support with the version numbers of the software you are running.