upr-rebalance fail during get_upr_backfill_remaining_items

Rebalance in 3 nodes while loading data 50k items.
Fails and UI log gives reason:

Rebalance exited with reason {unexpected_exit,
{'EXIT',<0.5506.0>,
{{noproc,
{gen_server,call,
['ns_memcached-ns_server:n_0@192.168.1.134->n_3@127.0.0.1:default',

{get_upr_backfill_remaining_items, "default",7}

,
180000]}},
{gen_server,call,
[

{'janitor_agent-default', 'n_0@192.168.1.134'}

,
{if_rebalance,<0.5484.0>,
{wait_upr_data_move,
['n_3@127.0.0.1','n_2@127.0.0.1'],
7}},
infinity]}}}}

TESTCASE:
python testrunner -i upr.ini -t rebalance.rebalancein.RebalanceInTests.rebalance_in_with_ops -p nodes_in=3,items=50000