[BUG] Delayed response to backend

[Bogay]

Describe the bug
Sometimes, sandbox sends submission result to BE server with terrible delay.
On the current NOJ server, there is one submission 5e90678f40be7cbfe207281b on sandbox-0 which is delayed about 10 mins after finish judgment, but it is sent to BE after the other submission immediately, maybe this is the reason?
here is part of logs:

# this is the moment 5e90370440be7cbfe20715b2 finish judgment
[2020-04-10 12:31:42 +0000] [7] [INFO] finish task 5e90370440be7cbfe20715b2/0108
# recieve another submission
[2020-04-10 12:33:37 +0000] [7] [INFO] receive submission 5e90678f40be7cbfe207281b.
# 2 submissions send to BE almost the at same time
[2020-04-10 12:33:46 +0000] [7] [INFO] send 5e90678f40be7cbfe207281b to BE server
[2020-04-10 12:33:46 +0000] [7] [INFO] finish submission 5e90678f40be7cbfe207281b
[2020-04-10 12:41:32 +0000] [7] [INFO] send 5e90370440be7cbfe20715b2 to BE server
[2020-04-10 12:41:56 +0000] [7] [INFO] finish submission 5e90370440be7cbfe20715b2

To Reproduce
Unknown.

Expected behavior
Send the result to BE server as soon as the judgment finishing.

Current Behavior
Delayed about 10 mins.

Possible Solution
I don't know...

Sandbox Version
249eb42

[asef18766]

is it a version with mutiple sandbox?

[Bogay]

these submissions are only sent to sandbox-0, so I just check the version of it.