If they work in that temporary location it does add to the belief the strength/reliability of the wireless signal isn’t getting to them in their normal location.
I don’t know the layout of your home, the location of your speakers, or the construction material for the property. Start with this: What are the “distances” and walls/obstructions between each of Playbase, Play:5, Boost, and Symfonisks? Do you have any other Sonos components? Where are they located? Which are Ethernet wired and which are on SonosNet?
For a moment I’ll assume the Play:5 is closer to the Playbase than the Symfonisks.
If you move the Boost closer to the Playbase does that help the Play:5, even if the Symfonisks get worse? Or, if you move the Boost into a different room from the 5?
If that does get the 5 working, the nature of SonosNet might then help the Symfonisks.
If not, is there any way you could at least temporarily run an Ethernet cable to one of the Symfonisks or the 5 in their normal location, to see what happens?