diagnostic why Dead lock happen on Exclusive waiting for update lock

met the following problem about deadlock, don't know whey this happens, need help, thanks! Here is what happens(the simplified version).

I have the following table and indexes:

--Create table JobMasterCREATETABLE[dbo].[JobMaster]([JobId] uniqueidentifier,[CreateTime] datetime NOTNULLDEFAULT(GETUTCDATE()),\[JobStatus] INT NULL,[JobStatusUpdateTime] DATETIME NULL,PRIMARYKEYNONCLUSTERED([JobId]))
GOCREATECLUSTEREDINDEX index_jobMaster_createtime ON[dbo].[JobMaster]([CreateTime])
GOCREATENONCLUSTEREDINDEX index_jobMaster_jobStatus ON[dbo].[JobMaster]([JobStatus])
GOCREATENONCLUSTEREDINDEX index_jobMaster_jobStatusUpdateTime ON[dbo].[JobMaster]([JobStatusUpdateTime])
GO

And we have a dead lock on three sessions: Deadlock: A ->(wait for resource holding by) B -> C -> A.

A and C holding the update lock on JobMaster with index PK (non-cluster), and session B holding the X lock on JobMaster with cluster index

Here is the operation for A/B/C(Read committed isolation level, no special setting): A/B:

UPDATE[JobMaster]SET[DataUploadStatus]=1,[DataUploadTime]= GETUTCDATE(),[PacketCount]=1,[RawDataSize]=1,[CompressedSize]=1WHERE JobId='E6AEE804-6A09-4293-B93C-15E9748E46ED'

C:

UPDATE[JobMaster]SET[JobStatus]=1,[JobStatusUpdateTime]= GETUTCDATE()WHERE JobId='E6AEE804-6A09-4293-B93C-15E9748E46ED'

My question is:

1. Why does session B wait on the U lock of jobmaster on pk index hold by A, while B is holding the X lock on clustered index? I mean since B has the X lock, which is lock to update the clustered index, seems it has no other locking needs?

2. What is the sequence of lock request/release on the three sessions? My understanding is, like for session B: update lock on JobMaster with PK and JobMaster with cluster index, then the X lock on JobMaster with Cluster index. Correct me if I am wrong.

3. Since we don't modify the non-cluster indexes, in any of the queries. Why do they need a U lock on the index? And why C is waiting for A, as C already have the U lock.