[can't connect to Cura but printer is actually connected.]

I was working on Cura 3.6 (with current firmware) but now on Cura 4.0, having trouble connecting to the existing printer (only change was to upgrade to 4.0).  Worked yesterday, not today after restarting Cura.  Browser can access the printer (Swagger APIs work, camera shows, etc) but Cura only has the option to "Save to File" after slicing.

 

Adding the same printer again seems to have tricked it into working.  Restarting Cura, the printer no longer works again.  Adding the printer yet again (3 printers now all point to the same printer) made it work again.

[System Date & Time ?]

Yes, odd that there'd be user facing interface dependent upon time from the printer compared to time in the browser client if you can't set the printer to something real.  I went through the swagger API list and haven't found anything yet to set date/time or, better yet, have it point to an NTP server.

[Ultimaker S5 - Constantly says it's out of filament, when it's not...]

I'm having the same issue with our S5.  It seems to be mostly one specific filament type (blue Matter Hackers PLA).  I'm curious what the S5 is actually checking since it mainly seems to be this one filament.  I've tested the friction in the Bowden tube, drag of the spool itself, cleaned the extruder, changed the extruder.  This filament is also having trouble "sticking" so I suspect the problem may be related.  During the print, the layers will separate.  If the printer pauses, it will most certainly result in a failed print due to layer separation. 

 

Since the printer is in a server room, the temperature is well regulated though if the cause were temperature variations, I'd expect it would affect more filaments.

[UM3 Extruded Tons of Polycarbonate Above the Rubber Seal----Welp!]

Where does one get the rubber seal replacements?  I must be searching the UM site wrong because I have not found it in spare parts or on the 3rd party sites.  I'm working with an S5 which came with 3 spares.  Down to the last spare and I think a good rubber seal is what helps avoid the situation in this thread.