If you are adding many realms to one signing URL or you have a large customized sign-in page or notifications configured, the Pulse desktop client stays in connecting status and the connection fails after some time. All this information is included in EAP packets send to the pulse desktop client. The maximum length of the EAP packet is 3600 Bytes.
You can configure many realms in one sign-in URL or you can have a customized Sign-in page, unless it is not exceeding the number of characters or length set by an upper limit of framed MTU of EAP response, ie 3600 Bytes.
This is applicable only for PDC-based connections and not for web-based connections. The web-based connection does not have any such limitations.