Significant in the report is that the say Ukrainian crash investigators did spend a few hours at the site in the first days. Unknown to anyone.
Sorry, what I can read is stating something slightly different...
Immediately following the crash of flight MH17, aviation investigators from Ukraine began investigating the cause of the accident.
...
on the days following the incident ... Ukrainian aviation investigators visited the crash site briefly several times
This does not mean they were searching the wreakage, they may have just looked at the ATC recording etc. and may have just took a first glance at the crash site. It is not surprising, that Ukranian investigators did their job.