We are suddenly seeing this on all our applications. We only have one DP. I've checked and tried several things suggested in similar posts.
1) Reviewed Boundaries and Boundary Groups. We have and have always had just one of each. The Boundary is our Active Directory site. The Boundary Group has one member (the AD site Boundary). The DP properties show the correct BG. Allow fallback is checked.
2) Rebuilt and redeployed a couple apps making sure to set Distribution Settings to "Distribute the content for this package to preferred DP and on the deployment type > Content "Allow clients to use a fallback source location"
3) I'm able to validate content on the DP.
On the client when I initiate an application install the CITaskMgr.log shows these steps and then hangs
Initiating task ContentDownload for CI ScopeId_FDACB1B1-2101-4440-91D1-C629993F101A/DeploymentType_53a4082c-dc3e-45b0-a2cc-d5b82980b0c7.2 (Adobe Flash Player 18 ActiveX - Windows Installer (*.msi file)) for target: S-1-5-21-4126972660-1444613362-1723402297-1195, consumer: {631E4A7C-A037-4FD3-8760-BC85FE1F6A91} CITaskMgr5/12/2016 12:18:03 PM1052 (0x041C)Initiating content download : CITask(ScopeId_FDACB1B1-2101-4440-91D1-C629993F101A/DeploymentType_53a4082c-dc3e-45b0-a2cc-d5b82980b0c7.2.S-1-5-21-4126972660-1444613362-1723402297-1195.Install.ContentDownload)CITaskMgr5/12/2016 12:18:03 PM1052 (0x041C)
State transition to (InProgress), Param(0) : CITask(ScopeId_FDACB1B1-2101-4440-91D1-C629993F101A/DeploymentType_53a4082c-dc3e-45b0-a2cc-d5b82980b0c7.2.S-1-5-21-4126972660-1444613362-1723402297-1195.Install.ContentDownload)CITaskMgr5/12/2016 12:18:03 PM1052 (0x041C)
State transition to (InProgress), Param(0) : CTaskConsumer(ScopeId_FDACB1B1-2101-4440-91D1-C629993F101A/DeploymentType_53a4082c-dc3e-45b0-a2cc-d5b82980b0c7.2.{F1C88031-A99C-4470-A0B8-C6282387E312})CITaskMgr5/12/2016 12:18:03 PM1052 (0x041C)
Successfully initiated contents download request {2F821282-514A-4C63-949D-0DFA0402B967} : CITask(ScopeId_FDACB1B1-2101-4440-91D1-C629993F101A/DeploymentType_53a4082c-dc3e-45b0-a2cc-d5b82980b0c7.2.S-1-5-21-4126972660-1444613362-1723402297-1195.Install.ContentDownload)CITaskMgr5/12/2016 12:18:03 PM1052 (0x041C)