Server Information
osTicket Version v1.16.5 (b48bf7e) — Up to date
Web Server Software Microsoft-IIS/10.0
MySQL Version 5.5.45
PHP Version 8.0.0
PHP Extensions
gdlib Used for image manipulation and PDF printing
imap Used for email fetching
xml XML API
xml-dom Used for HTML email processing
json Improves performance creating and processing JSON
mbstring Highly recommended for non western european language content
phar Highly recommended for plugins and language packs
intl Highly recommended for non western european language content
fileinfo Used to detect file types for uploads
zip Used for ticket and task exporting
APCu Improves overall performance
Zend Opcache Improves overall performance
PHP Settings
cgi.fix_pathinfo "1" is recommended if AJAX is not working
date.timezone Europe/Athens
Database Information and Usage
Schema osticket (ticketsrv)
Schema Signature c37e165651dc289240fee7d244990ac1
Space Used 412.55 MiB
Space for Attachments 218.50 MiB
Timezone GTB Standard Time (Interpreted as Asia/Beirut)

I think I found a bug.
At least in my installation, it happens.
When I write the note or reply and then upload the attachment, everything works fine.
If I upload the attachment and then type the text, the attachment disappears after the post and nobody receives it.