They stuck to me like glue - even Cyclops that I could normally outrun - eg if I had no "offensive" cargo and was cold, I could run at any speed and they would keep with me till scan complete - then lose interest and I could take samples etc. Exact same ship if I decided to go "hot" and, say nick an escape pod from it (they really hate that) - would make it come after me - but I could easily outrun it.
No matter what combination I tried, I've never been able to shake of an initial Thargoid scan on entering a USS - and I have somewhere north of 60 thargoid ship signature scans in my data bank and I don't even scan most of them - so I've tried this a lot

I can high wake on them, and I can do what I like "after" intial scan, I even came within 8% of soloing one (and I'm not that interested in killing them as such)- but, damned if I can "sneak" in on them to start with.
I always play "rogue" types and like my stealth so have been trying to find the best way's of sneaking around the bugs and pickpocketing them - so far the arrival in a USS seems to allow them to auto lock in on you - you can be an ice cube with zero running - and they will come right to you -after scan they can't see past 1k range if your stealthy.