OK, probably found it.
In Prod-oVirt we had VMs with disk which were direct luns, iscsi luns.
They are still in the system, either attached but inactive to VMs or as
unattached disks.
Seems that some attribute from those disk is crashing rbovirt.
I did a little cleanup on xml.inspect from volume.rb and result is below.
<Nokogiri::XML::Element:0x47b916c name="disk"
attributes=[#<Nokogiri::XML::Attr:0x450aeac name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a">,
#<Nokogiri::XML::Attr:0x450ae84 name="id" value="555af736-81d6-4334-a187-33122f3e445a">]
children=[#<Nokogiri::XML::Text:0x4783c10 "\n ">,
#<Nokogiri::XML::Element:0x4783850 name="actions" children=[#<Nokogiri::XML::Text:0x46d73d4 "\n ">,
#<Nokogiri::XML::Element:0x46d703c name="link" attributes=[#<Nokogiri::XML::Attr:0x46d6d08 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/deactivate">,
#<Nokogiri::XML::Attr:0x46d6bf0 name="rel" value="deactivate">]>,
#<Nokogiri::XML::Text:0x478da94 "\n ">,
#<Nokogiri::XML::Element:0x478d8a0 name="link" attributes=[#<Nokogiri::XML::Attr:0x478d800 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/activate">,
#<Nokogiri::XML::Attr:0x478d774 name="rel" value="activate">]>,
#<Nokogiri::XML::Text:0x47e4c54 "\n ">,
#<Nokogiri::XML::Element:0x47e49d4 name="link" attributes=[#<Nokogiri::XML::Attr:0x47e47b8 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/export">,
#<Nokogiri::XML::Attr:0x47e4790 name="rel" value="export">]>,
#<Nokogiri::XML::Text:0x47f82e0 "\n ">,
#<Nokogiri::XML::Element:0x47f7b10 name="link" attributes=[#<Nokogiri::XML::Attr:0x47f7804 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/move">,
#<Nokogiri::XML::Attr:0x47f77b4 name="rel" value="move">]>,
#<Nokogiri::XML::Text:0x48097fc "\n ">]>,
#<Nokogiri::XML::Text:0x4808adc "\n ">,
#<Nokogiri::XML::Element:0x47b81f4 name="name" children=[#<Nokogiri::XML::Text:0x4813e8c "doc01_Disk1">]>,
#<Nokogiri::XML::Text:0x481357c "\n ">,
#<Nokogiri::XML::Element:0x4812f00 name="link" attributes=[#<Nokogiri::XML::Attr:0x4812bf4 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/permissions">,
#<Nokogiri::XML::Attr:0x4812bb8 name="rel" value="permissions">]>,
#<Nokogiri::XML::Text:0x48205b0 "\n ">,
#<Nokogiri::XML::Element:0x482022c name="link" attributes=[#<Nokogiri::XML::Attr:0x4820100 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209/disks/555af736-81d6-4334-a187-33122f3e445a/statistics">,
#<Nokogiri::XML::Attr:0x48200ec name="rel" value="statistics">]>,
#<Nokogiri::XML::Text:0x481e968 "\n ">,
#<Nokogiri::XML::Element:0x4824930 name="vm" attributes=[#<Nokogiri::XML::Attr:0x4824854 name="href" value="/api/vms/efa0c18a-3c4c-44fd-9758-4bd25579f209">,
#<Nokogiri::XML::Attr:0x4824818 name="id" value="efa0c18a-3c4c-44fd-9758-4bd25579f209">]>,
#<Nokogiri::XML::Text:0x474ae4c "\n ">,
#<Nokogiri::XML::Element:0x474acbc name="alias" children=[#<Nokogiri::XML::Text:0x4521198 "doc01_Disk1">]>,
#<Nokogiri::XML::Text:0x45206d0 "\n ">,
#<Nokogiri::XML::Element:0x4520068 name="interface" children=[#<Nokogiri::XML::Text:0x45020f4 "virtio">]>,
#<Nokogiri::XML::Text:0x4501898 "\n ">,
#<Nokogiri::XML::Element:0x4501514 name="bootable" children=[#<Nokogiri::XML::Text:0x4500a74 "false">]>,
#<Nokogiri::XML::Text:0x4696820 "\n ">,
#<Nokogiri::XML::Element:0x4696460 name="shareable" children=[#<Nokogiri::XML::Text:0x469608c "false">]>,
#<Nokogiri::XML::Text:0x4695a88 "\n ">,
#<Nokogiri::XML::Element:0x46957a4 name="wipe_after_delete" children=[#<Nokogiri::XML::Text:0x46874d8 "false">]>,
#<Nokogiri::XML::Text:0x4686a4c "\n ">,
#<Nokogiri::XML::Element:0x468618c name="propagate_errors" children=[#<Nokogiri::XML::Text:0x4685a70 "false">]>,
#<Nokogiri::XML::Text:0x439e668 "\n ">,
#<Nokogiri::XML::Element:0x439e280 name="active" children=[#<Nokogiri::XML::Text:0x439d934 "false">]>,
#<Nokogiri::XML::Text:0x439d2e0 "\n ">,
#<Nokogiri::XML::Element:0x40cf2ac name="read_only" children=[#<Nokogiri::XML::Text:0x40cee24 "false">]>,
#<Nokogiri::XML::Text:0x40ce938 "\n ">,
#<Nokogiri::XML::Element:0x40ce7e4 name="lun_storage" attributes=[#<Nokogiri::XML::Attr:0x40ce730 name="id" value="36090a01840ec6ccb8be664f48b00e04c">]
children=[#<Nokogiri::XML::Text:0x4654038 "\n ">,
#<Nokogiri::XML::Element:0x4653a0c name="logical_unit" attributes=[#<Nokogiri::XML::Attr:0x46538f4 name="id" value="36090a01840ec6ccb8be664f48b00e04c">]
children=[#<Nokogiri::XML::Text:0x4652bc0 "\n ">,
#<Nokogiri::XML::Element:0x4652850 name="serial" children=[#<Nokogiri::XML::Text:0x4865afc "SEQLOGIC_100E-00_6090A01840EC6CCB8BE664F48B00E04C">]>,
#<Nokogiri::XML::Text:0x486541c "\n ">,
#<Nokogiri::XML::Element:0x4865278 name="vendor_id" children=[#<Nokogiri::XML::Text:0x4864f94 "EQLOGIC">]>,
#<Nokogiri::XML::Text:0x4864b34 "\n ">,
#<Nokogiri::XML::Element:0x48649b8 name="product_id" children=[#<Nokogiri::XML::Text:0x4864508 "100E-00">]>,
#<Nokogiri::XML::Text:0x4504ea8 "\n ">,
#<Nokogiri::XML::Element:0x4504c3c name="lun_mapping" children=[#<Nokogiri::XML::Text:0x4504340 "0">]>,
#<Nokogiri::XML::Text:0x4503b5c "\n ">,
#<Nokogiri::XML::Element:0x45038f0 name="size" children=[#<Nokogiri::XML::Text:0x468b8e4 "10737418240">]>,
#<Nokogiri::XML::Text:0x468b380 "\n ">,
#<Nokogiri::XML::Element:0x468b1dc name="paths" children=[#<Nokogiri::XML::Text:0x468adb8 "0">]>,
#<Nokogiri::XML::Text:0x468a804 "\n ">,
#<Nokogiri::XML::Element:0x468a46c name="disk_id" children=[#<Nokogiri::XML::Text:0x468a0fc "555af736-81d6-4334-a187-33122f3e445a">]>,
#<Nokogiri::XML::Text:0x4689e18 "\n ">]>,
#<Nokogiri::XML::Text:0x48b343c "\n ">]>,
#<Nokogiri::XML::Text:0x48b2c30 "\n ">]>