I had a live migration issue with windows too.
Secondary host running XCP-ng 7.5, primary XS7.1, live-migrated the Win 2K12 VM from primary host to secondary fine, took 14mins. I updated XS7.1 to XCP-ng 7.5 and installed new Dell BIOS on primary host. Migrate back hung at 99%. I left it about 45mins (3-times as long as the original migrate took) and noted it was still sending data between the two.. I wonder if it was stuck in some form of loop.
The logs on src host had this in logs a lot:
Aug 16 13:55:05 xen52 xenopsd-xc: [debug|xen52|37 |Async.VM.migrate_send R:c6ab32165e47|xenops_server] TASK.signal 1305 = ["Pending",0.99]
Aug 16 13:55:05 xen52 xapi: [debug|xen52|389 |org.xen.xapi.xenops.classic events D:333a26fc4942|xenops] Processing event: ["Task","1305"]
Aug 16 13:55:05 xen52 xapi: [debug|xen52|389 |org.xen.xapi.xenops.classic events D:333a26fc4942|xenops] xenops event on Task 1305
Aug 16 13:55:05 xen52 xenopsd-xc: [debug|xen52|37 |Async.VM.migrate_send R:c6ab32165e47|xenops] VM = 66ebe30b-2bd2-ae59-c225-54a625655d52; domid = 2; progress = 99 / 100
I read a bit on Citrix forums and decided to shutdown the VM. Doing so from XCP-ng center didn't work, so I did it from within the VM.
Upon shutdown it seemed to sort itself, but the VM came up as 'paused' on the primary node. This couldn't be resumed. A force restart from XCP-ng center jsut seemed to hang. I tried to cancel the task with xe task-cancel on hard_reboot and it didn't work so did a xe-toolstack-restart and this reset the VM state back to shutdown. It then booted normally...
Now the secondary host was running an old BIOS still with earlier microcode so not sure if it was related to that in anyway..