I've done something similar and haven't experienced that issue but try running the count on the actual field as below and add the where clause if you're not using the time range picker on the Search UI.
eventtype=jira (issuetype="Bug" OR issuetype="Defect") AND fields.created=*
| spath fields.created
| dedup key
| stats count(fields.created)
| where fields.created>=relative_time(now(),"-7d@d")
If fields.created is not in EPOCH then you can use something similar to the line below - you'd put this line in after the dedup.
|strptime(fields.created, "%Y-%m-%dT%H:%M:%S")
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