Your browser could be dropping the connection after it finishes the bundle downloads. If you grab a bandwidth monitor, you can see if that is the case (just Google it, there are a ton of free simple ones that do the trick).
If it IS dropping the connection (once the download completes, the data transfers drop to under 1kb each way and doesn’t come back), then you could try the trick I use. Pull up one browser that will have to download the bundles and another with them already cached (I play in FireFox and use Chrome as the backup since it only has some of the bundle). Bring them both to the server list. Open up the server you want in the browser without the files cached, then click on the same server in the other browser.
Once the browser with the cached files loads all the files, it should connect to the server, then just close the other browser.
Basically what you are doing is forcing a connection to persist by using the extra browser. It maintains the data flow, and the cached browser’s data piggybacks on the other browser’s link.
I have never figured out why data connections will just arbitrarily drop after a certain point (which happens ALL over the web), but I’ve found the best way to fix it is to create a redundant data channel for the cached browser to piggy back off and it’s never failed me. Just remember to disconnect the redundant channel once the game loads up and connects so you aren’t using two spots on the server (as that’s very wasteful and doesn’t help the devs).