You might want to look into post #11 here:
https://forum.kodi.tv/showthread.php?tid=374120
Click on the links so that they open in new tabs (so you can cross reference), but the key thing to understand is that PlutoTV (because we're not signing in to an account) is
probably getting a UDP broadcast or multicast datastream, and the internet architects built a specialized lane for Real Time Streaming, and some protocols around it.
(click on my link to the IPv6 wiki page if you're new to IPv6 to see why in this streaming world, it's probably a good idea to use it if it's available to you.)
On my router, I had to forward the port on the IPv4 side, and open it on the IPv6 firewall, and send that traffic on the WAN through a specific port on the LAN, Then in IPTV Simple set it up to listen to that LAN port
don't forget to config SlyGuy Common Playback options.
Once I paid attention to this stuff and made a few simple (to me - I understand a little of this stuff) config adjustments, it started to get significantly more reliable. (and PlutoTV itself seems to prefer streaming over IPv6, or seems to
to me)