Deadlock found in create feedback API

**Gorse version**
v0.4.4-5-gf4a6606

**Describe the bug**
I use the Logstash to read from the SQL Server database and insert feedback into the gorse system via API (HTTP output plugin). I get the following error on the API call

_Error 1213: Deadlock found when trying to get lock; try restarting transaction_

**To Reproduce**
http {
url => "http://192.168.20.208:8087/api/feedback"
http_method => "post"
format => "json_batch"
}

**Expected behavior**
status: 200
response: affected rows number