If you mean issues in that private security guards did not always do the right thing in other states, then the reports are that some did not.
Were health workers actually doing the security interstate or was it more a mixture of police, ADF and private security guards? Not that I have really researched exactly what each did, but many articles that I have read indicated that security was done by a mix of the latter 3 groups and not healthcare workers. Use of private security guards seems to have been widesread.
Indeed it can take only one, or in Victoria may be two as rumour has it that there may be two different genomic sources of the second wave in Victoria.
And screening out people who might have sex with people under there car is not so easy. Police, healthcare workers, priests, teachers have all at times been found wanting.
With Victoria it could well get down to the key difference being that two security guards may have had sex with two quarantine guests and thus each caught the virus. It could well be without these acts, if they occurred, that the other dominos to spread the the virus out into the community would not have fallen. We may well have never have had the second wave.
This part if it occurred I doubt anyone could have predicted. Now I am in not saying the contracts were done properly in Vic as they clearly were not, but not all in life can be foreseen.
From what I have read there have been quarantine breaches in many states. Though in Victoria the consequences have been disastrous.
PS:
Security guards in NSW were sacked for sleeping on the job. There are reports of sleeping guards from May till June.
A private Security Guard hard at work at a Sydney Quarantine Hotel, and who also seems to be lacking PPE.