I installed TI from Softaculous to evaluate in depth because we have several small local restaurants as clients, and when I go to the admin login I enter the credentials I set and the "Login Admin Panel" page simply refreshes itself exactly as it was with empty username and password fields. I tried using the admin name I set during installation as well as the email I set. Several times.
So I uninstalled, re-installed, ensured I had exact copies of all credentials, and tried again. Same result. Rinse and repeat for about 10 fresh installations now with no change. Tried leaving all credentials as default as well and just copying them. No change. Install goes fine, main login shows up fine, admin login shows up fine... it just doesn't do anything. At all. No variation on the credentials I use during install return anything except fresh fields. No errors, no access.
Leaving the admin login fields blank returns errors that Username field and Password field are required, so the form is definitely sort of working and connecting to the DB on some level, but no approach to logging in gets me through the front door.