May be on unoconv and JPG there are hints in these discussions:
- Unoconv not converting jpeg to PDF https://moodle.org/mod/forum/discuss.php?d=399755
- unoconv and HEIF image problems https://moodle.org/mod/forum/discuss.php?d=415781
- Unoconv not converting some file types https://moodle.org/mod/forum/discuss.php?d=402880
- Unoconv not converting jpeg to PDF https://moodle.org/mod/forum/discuss.php?d=399755
- unoconv and HEIF image problems https://moodle.org/mod/forum/discuss.php?d=415781
- Unoconv not converting some file types https://moodle.org/mod/forum/discuss.php?d=402880
Note: Your issue is unlikely to be to related to performance. Therefore better suited for General help forum rather than Hardware and performance.