All three countries, Italy, Slovenia and Croatia are in the Schengen area. There are no regular immigration checks on the borders between those countries. I have often seen 'random' immigration checks by Italian police on the Slovenian/Italian border, which seem less random and more permanent, but they only check persons travelling in the other direction. You do not have to expect any immigration checks in the direction you are travelling.

As long as you stay within the Schengen area, you can travelling between the countries without each border crossing to be counted as an 'entry' on your Schengen visa. Even with a single entry visa, you could have done this bus trip without issues.

All three countries, Italy, Slovenia and Croatia are in the Schengen area. There are no regular immigration checks on the borders between those countries. I have often seen 'random' immigration checks by Italian police on the Slovenian/Italian border, which seem less random and more permanent, but they only check persons travelling in the other direction. You do not have to expect any immigration checks in the direction you are travelling.

As long as you stay within the Schengen area, you can travel between the countries without each border crossing to be counted as an 'entry' on your Schengen visa. Even with a single entry visa, you could have done this bus trip without issues.