When adding attachments (in JSD queue view), Jira automatically increments + appends a number suffix even if the file does not exists

Issue Summary

When adding attachments in JSD, JSD automatically increments + appends a number suffix even if the file does not exists

Steps to Reproduce

1. Jira 8.6.0/JSD 4.6.0
2. Browse > select files, in the "Add attachment" pop up, cancel the the upload
3. Do the same thing again, observe that the number suffix is added, it is also incremented if this is operation is done repeatedly.
4. Try creating a new issue, perform the same steps above and observe the number suffix is added, even if the attachments do not exist on the new issue.

Video clip demonstration: Recording #4.mp4

Additional note:

• Once the above happens, try attaching the same files in another Business or Software type project, the number suffix will also be automatically added, even on a different project type/issue.

Expected Results

Jira should not append the number suffix, since the attachment with the same name does not exists.

Actual Results

Jira appends a number suffix, even on a new issue without any attachments

Workaround

Disable the following feature flags in Jira.
sd.attachment.generate.unique.suffix.when.attachment.filename.clash.occurs
com.atlassian.jira.attachments.generate.unique.suffix

This should look like this: 

Read how to do this here: https://confluence.atlassian.com/jirakb/enable-dark-feature-in-jira-959286331.html