I am going to guess, you are seeing what Experian refers to as a "mixed" file. While I don't know entirely "why" this happpens other than someone/somewhere/something is either close (meaning name, address, SS or other identifier) or has been mis-typed and you are getting mixed results on Experian. If sometimes you get the data and it's accurate and other times you don't...that tells me that EX has/is getting the info, but what you're getting presented is inaccurate.
My idea would be start by calling them, yes I know how painful that is....and explain that you are experiencing an issue that sounds like a mixed file. The words "mixed file" are part of their own venacular so they will understand what that means and launch an investigation to sort it out. This could lead to 2 results....the simplest being they acknowledge their error and correct it. The other and more time intensive response is them stating they are reporting the info reported by XX and you'll need go through all your accounts and determine who has incorrect info being fed to EX on a regular basis. If result #2 is the answer, suffice to say you will likely have this issue in other places and with other reporting agencies..not just the main 3 but also, outliers like Chexsystems and LexisNexis/Sagestream.
https://www.experian.com/blogs/ask-experian/acr-faqs/acr-inaccuracies-in-reporting/
