The phrase "unreliable indicator" means that something is not trustworthy or accurate in showing or predicting a certain outcome or situation. Full definition
They cite research showing the tests are unreliable indicators of what is happening in classrooms, particularly when based on just a year of data. (washingtonpost.com)
Reviews are an extremely unreliable indicator of quality. (studiotendra.com)
With Conwert owning 96 %, I suspect the share price is a pretty unreliable indicator — I presume it only remains listed so Conwert can keep its options open (for itself, or a potential buyer). (wexboy.wordpress.com)