There should always be 5 empty channels between the channels you use for your WiFi equipment. And as WiFi equipment is only allowed on 11 channels (except for Japan, they have 13 WiFi channels), you can have 3 options in that range: 1, 6 and 11. Any other combination leaves you only only 2 channels to choose from.
Also, when your neighbor has WiFi, say for example on channel 1, the closest WiFi node in your network should use channel 6 or 11. If you have more than one WiFi device in your house, you have to alter the channels so they don't interrupt the WiFi network of your neighbor. Why that consideration? Well, as you are clearly more aware then they do, you can work around these obstacles. And it will end up in a better WiFi covered network for yourself. It also prevents your neighbor to buy repeaters for "getting a stronger signal" where they need it to be.
More often than not, the signal strength of the WiFi device is set to "strong". Depending on the location of your and their WiFi devices, these can drown out the WiFi signal for both you and your neighbor. Which is then "solved" by repeaters, creating an even bigger mess. And, as there is a great variance between signal strength of WiFi devices, this can become a problem.
If your whole mesh system started to fail without changing anything on your end, it might be because of the neighbor adding things to his WiFi network, started using a microwave close by or you are troubled by other (external) sources of disruptions. It might prove prudent to investigate this further, before investing (heavily ?) in a new WiFi mesh system. Because external disruptions can occur at any given time you can never be really sure that you have "fixed" the mesh part. Remember, when WiFi devices are set to "Auto" with their channel selection, they select the best channel at the moment they are turned on. This does not change anymore and if another device with a static channel is turned back on, both devices won't work properly anymore. Either go full "auto" with every WiFi device in your place and from all your neighbors, or manage it properly by selecting channels 1, 6 or 11 for your own network as well as those from your neighbors. Going "Auto" might sound simpler, but it will always result in a mess. Once you have your and your neighbors channels set up correctly, you will see that the WiFi networks everywhere will work a lot better.
Best thing to do, in my not so humble opinion, is to dump mesh. WiFi is crap to begin with. Mesh hardly improves on that, even with separate backhaul channels on different frequencies. WiFi is nothing more than radio signals on either a very congested frequency or a frequency that doesn't carry very far. Those separated frequencies might help for a while, but it is sub-par at best.
As a sufferer (read: maintainer) of WiFi networks, I have spent way too much time finding out why WiFi signals stop working. After the umpteenth complaint about: "WiFi doesn't work!" from colleagues, friends and family members, I got very fed up with the crap that is WiFi. Now I have one UTP cable running through the house, as much out of sight as I could get it and setup WiFi routers to be dumbed down to Access Point duties. The UTP cable is a daisy chain between these WiFi routers and the ISP's modem. Sure, it wasn't fun setting those up. Or getting questioned the whole time by better halves to make sure the cable is invisible.
However, even those persons stopped complaining about a piece of cable being in sight somewhere, as WiFi became much more reliable. 3 WiFi routers as AP for an area 90 meters wide and 90 meters deep. Often with 20 people or more (pre-Covid) and guess what? No-one is complaining about WiFi not working anymore. Do yourself a real favor, use a UTP cable as backhaul, don't trust WiFi to be capable of this, it simply isn't, no matter how much the manufacturer of that type of equipment wants to sell their product to you.
You can even run this cable around the house, if you and/or partner is appalled by having such a cable inside your house. But whatever you do, don't waste more time and money on WiFi than you have to.
