Sql-server – Seeing 2 exclusive locks on the same index – is this possible

Please help me understand how it is possible that I am seeing 2 exclusive locks on the same index. This is on SQL Server 2012 SP3. It is from within a vendor application and don't know how transaction settings are working. Oh, and this is on SELECTs!

Here is a picture from SQL Sentry's monitoring:

The deadlock graph details are here:

<deadlock>
  <victim-list>
    <victimProcess id="process3dd4558" />
  </victim-list>
  <process-list>
    <process id="process3dd4558" taskpriority="0" logused="968" waitresource="KEY: 10:72057594054049792 (34375086fdb7)" waittime="3723" ownerId="1155141462" transactionname="implicit_transaction" lasttranstarted="2016-10-18T18:49:28.763" XDES="0x1c5b81b6a8" lockMode="S" schedulerid="5" kpid="2968" status="suspended" spid="257" sbid="0" ecid="0" priority="0" trancount="1" lastbatchstarted="2016-10-18T18:49:28.770" lastbatchcompleted="2016-10-18T18:49:28.770" lastattention="1900-01-01T00:00:00.770" hostname="host4" hostpid="0" loginname="host4user" isolationlevel="read committed (2)" xactid="1155141462" currentdb="10" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128058">
      <executionStack>
        <frame procname="adhoc" line="1" stmtstart="144" sqlhandle="0x02000000a9eef71a951d683a59623271b0518177293509aa0000000000000000000000000000000000000000">
        SELECT fulfillmentid, distid, transid, transtime, signref, loanuntil, userid, confirmed, returnable, returned FROM fulfillment WHERE ((fulfillment.userid = @P0) AND (fulfillment.returnable = @P1) AND (fulfillment.returned = @P2)) AND ((fulfillment.loanuntil IS NULL) OR (fulfillment.loanuntil &gt;= @P3))    </frame>
        <frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
        unknown    
    </frame>
      </executionStack>
      <inputbuf>
    (@P0 varbinary(8000),@P1 nvarchar(4000),@P2 nvarchar(4000),@P3 datetime)SELECT fulfillmentid, distid, transid, transtime, signref, loanuntil, userid, confirmed, returnable, returned FROM fulfillment WHERE ((fulfillment.userid = @P0) AND (fulfillment.returnable = @P1) AND (fulfillment.returned = @P2)) AND ((fulfillment.loanuntil IS NULL) OR (fulfillment.loanuntil &gt;= @P3))                                   </inputbuf>
    </process>
    <process id="process4158558" taskpriority="0" logused="4652" waitresource="KEY: 10:72057594054049792 (9c5f356ba0f3)" waittime="3723" ownerId="1155141461" transactionname="implicit_transaction" lasttranstarted="2016-10-18T18:49:28.763" XDES="0x2fa2ce8d28" lockMode="S" schedulerid="2" kpid="7032" status="suspended" spid="162" sbid="0" ecid="0" priority="0" trancount="1" lastbatchstarted="2016-10-18T18:49:28.770" lastbatchcompleted="2016-10-18T18:49:28.770" lastattention="1900-01-01T00:00:00.770" hostname="host4" hostpid="0" loginname="host4user" isolationlevel="read committed (2)" xactid="1155141461" currentdb="10" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128058">
      <executionStack>
        <frame procname="adhoc" line="1" stmtstart="144" sqlhandle="0x02000000a9eef71a951d683a59623271b0518177293509aa0000000000000000000000000000000000000000">
        SELECT fulfillmentid, distid, transid, transtime, signref, loanuntil, userid, confirmed, returnable, returned FROM fulfillment WHERE ((fulfillment.userid = @P0) AND (fulfillment.returnable = @P1) AND (fulfillment.returned = @P2)) AND ((fulfillment.loanuntil IS NULL) OR (fulfillment.loanuntil &gt;= @P3))    </frame>
        <frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
        unknown    
    </frame>
      </executionStack>
      <inputbuf>
    (@P0 varbinary(8000),@P1 nvarchar(4000),@P2 nvarchar(4000),@P3 datetime)SELECT fulfillmentid, distid, transid, transtime, signref, loanuntil, userid, confirmed, returnable, returned FROM fulfillment WHERE ((fulfillment.userid = @P0) AND (fulfillment.returnable = @P1) AND (fulfillment.returned = @P2)) AND ((fulfillment.loanuntil IS NULL) OR (fulfillment.loanuntil &gt;= @P3))                                   </inputbuf>
    </process>
  </process-list>
  <resource-list>
    <keylock hobtid="72057594054049792" dbid="10" objectname="xxxx.dbo.fulfillment" indexname="IX_fullfilment_userid_loanuntil_returnable_returned" id="lock3118a8ae80" mode="X" associatedObjectId="72057594054049792">
      <owner-list>
        <owner id="process4158558" mode="X" />
      </owner-list>
      <waiter-list>
        <waiter id="process3dd4558" mode="S" requestType="wait" />
      </waiter-list>
    </keylock>
    <keylock hobtid="72057594054049792" dbid="10" objectname="xxxx.dbo.fulfillment" indexname="IX_fullfilment_userid_loanuntil_returnable_returned" id="lockcffbaed80" mode="X" associatedObjectId="72057594054049792">
      <owner-list>
        <owner id="process3dd4558" mode="X" />
      </owner-list>
      <waiter-list>
        <waiter id="process4158558" mode="S" requestType="wait" />
      </waiter-list>
    </keylock>
  </resource-list>
</deadlock>

Also, if there is anything else I need to post, please let me know. Thank you.

The server is part of an AG set, we failed over today and the
deadlocks disappeared. Another mystery unsolved.