It appears that 0.58 shipped with a bug that caused a few people to scratch their heads for quite a while.
The bug caused sqlr-start to crash, sometimes, under very specific circumstances.
The first is if an instance is defined with no port and no socket (ie. falling back to the default port of 9000). This would fairly reliably crash.
The second is very intermittent. Basically, if you call sqlr-start by itself, with no id, expecting that it will start all instances where enabled="yes" is configured, it will crash. Sometimes. Depending on a lot of random things. It turned out that a few variables were uninitialized, and random crashing a fairly classic behavior in that case.
Both issues are fixed in the 0.58.1 release. So, if you've had problems like those with 0.58, then give 0.58.1 a try.
It can be downloaded here.