t2.micro probably is too small. I use a t2.medium for my sandbox. 100GB isn't enough, either. Try 300GB.
The message means Splunk is trying to index a non-text file and is informational. It should not prevent login. You can delete that file to clear the log message. Use less or more rather than vi to view log files.
There should be other log messages explaining why you can't log in.
I used t2.micro instance. I installed version downloaded version
splunk-8.2.6-a6fe1ee8894b-Linux-x86_64.tgz and I untarred it.
I have a UNIX volume of 100Gb.
Inside the file splunkd.log:
The file '/home/ec2-user/splunk/var/log/splunk/.sp lunkd.log.swp' is invalid. Reason: binary.