it is really annoying bug..
Absolutely true.. and it has been there for an age, 2 ages and half an age.. (to put it in bilblical proportions).
We have been fighting this since Lion. It is a hard one.. and as you note, makes little sense. The TC is not lost.. it has simple vanished as a file store to the computer.
There is no total bug fix.. sorry. 10.9.3 was supposed to improve the networking and fix it though.. cough.. gollum gollum.. cough.
I presume this has been happening going way back when??
1. I strongly recommend using 7.6.1 firmware.. but that is up to you.. now is the point to do it.. but you can start at point 2 instead and if that doesn't help go around again start at 1.
Downgrade to 7.6.1 firmware.. if the TC is old go back even further.. 7.5.2 for gen1 or gen2. Even maybe Gen3.
Downgrade by holding in option key when you select version. like thus.
2. Factory reset.
The Factory Reset universal
Unplug your TC/AE. Hold in reset. and power the TC/AE back on.. all without releasing reset and keep holding in for about 10sec. The time is not important.. it is the front LED rapid flashing that indicates you are in factory mode.
If it doesn’t flash rapidly you have released reset at some point and try again.
Be Gentle! Feel the switch click on. It has a positive feel.. add no more pressure after that.
TC/AE will reboot after a couple of minutes with default factory settings and will wipe out previous configurations.
No files are deleted on the hard disk.. No reset of the TC deletes files.. to do that you use erase from the airport utility.
3. All new setup.. Do not use old names.. Please clear out all the old names from your wireless on the laptop.
New names should be short, no spaces and pure alphanumeric. eg TCgen4 (or whatever gen it is) as base station name. Use simple name like TCwifi for the wireless or even separate names for each band, eg TC24ghz and TC5ghz. The less stuff left on auto the less stuff that can stuff up.
4. Manually mount the TC disk in the computer.. and I strongly recommend you do this by IP.. certainly if the TC is static, eg in router mode it is 10.0.1.1 by default and you should use that. It is better than using names. Even if the TC is bridged .. if at all possible make the TC ip static, via the dhcp reservations in the main router.
Then in Finder.. Go, Connect to server. (or address bar in safari for example will take you there).
or AFP://TCgen4.local (whatever your TCname plus the correct local domain, by default local. )
It will find the network resource.. ask for password.. type in your password.. remember to store it in your keychain.
Make sure ipv6 is set correctly in the computer and on the TC. There is a little known document where Apple makes it clear this is important.
On the TC it is under Internet tab.. options.. (why there and not networking.. I do not know)
(ignore the global domain.. I was trying that to also fix it but it seems to not work).
will doing all that fix it.. Maybe and possibly not..
It should however make the problem less acute.
No luck please give me more info on the whole network setup. Main modem.. make and model. TC actual model.. A1xxx from the base.
How the two are connected and how the TC is set .. bridge or main router. Or much worse double NAT or join wireless.
I have a few other ways to do things.. that might help when you have the TC in bridge mode.