Lync Push Notification not working in Mobile Clients

Most Of the time Lync URL Filter setting causing the issue.Blow option woked for me.Lets have a Try!
Option 1

1. Open the Lync Server Control Panel (LSCP)
2. Choose the IM and Presence feature from the LSCP menu
3. Select the URL Filter page button
4. On the Edit URL Filter - Global page, choose the Do not filter option as the Hyperlink prefix
5. Click on the Commit button

 Option  2

1. Open the Lync Server Control Panel (LSCP)
2. Choose the IM and Presence feature from the LSCP menu
3. Select the URL Filter page
4. Leave the Send warning message option chosen as the Hyperlink prefix
5. Click on the Select... button for the Filter these hyperlinks prefixes: feature
6. On the Select Hyperlink Prefix page, expand the HTTP Hyperlink prefixes
7. Remove the check mark from the http: and https: hyperlink prefixes
8. Click on the OK button
9. On the Edit URL Filter - Global page, click on the Commit button

Note the following Lync Server 2010 PowerShell cmdlets can be used to remove hyperlink prefixes using the Lync Server Management Shell:

• Set-CsImFilterConfiguration -Identity -Prefixes @{remove="http:"}
• Set-CsImFilterConfiguration -Identity -Prefixes @{remove="https:"}