Are arXiv papers more read than the journal versions? I have a conference paper which is published at IEEE with some errors unfortunately. But I have submitted a version on ArXiv without the errors.

As a researcher, I honestly prefer reading versions on ArXiv because I always think that if such an error has been detected by the authors in the official version (i.e., IEEE, Springer, etc.), they will of course have tried to correct it in their ArXiv version. That is why I usually prefer to read ArXiv versions or that ones present on the authors’ personal page.

Some researchers told me that papers on ArXiv (or HAL for example) are more read than the official versions. Is this true?
Well, statistically speaking, ArXiv requires no reader subscription, so more people have access to it (regardless of what publications they or their institute pays for). Ergo publications on ArXiv have the potential receive views from a wider audience. Whether this translates to citations or not is another argument.

It’s relatively common in my field to see an author "park" some research on ArXiv before submitting it to official publications or conferences. The publication process can take a while (and conferences have fixed dates), but the paper might as well gather interest and citations during that time.

I’ve never heard of anyone publishing on ArXiv after publishing in a journal, but I have seen post-conference extended papers (which go into more detail without the page limit). I don’t know what copyright you signed over (or what access level your publications have) when you published but I’d be wary about infringing the official publisher's copyright by posting on ArXiv. 

———————-Edit———————

Well, according to comments, some journals explicitly allow publishing to ArXiv (or related sites) after publication. That might depend on gold access level, but it makes sense for journals to make ArXiv an ally rather than an enemy. Relevant xkcd.