Will I have issues re-entering Thailand for the third time after short trips to Europe?

Your travel pattern might seem a bit odd to an immigration officer but if you have all your flights booked and can show them you shouldn't have an issue

No its amount of days in country not entries, if got flights for all should be no issue. Also they will be looking at previous years travel as well

Depends on the IO mood on the day im afraid

If you're entitled to a 60 days visa exemption entry and your two trips out are within these 60 days then you could buy a re-entry permit for each trip out, keeping your original 60 days alive

In itself, this travel pattern is normally fine. Short stays in Thailand with brief trips back to Europe for business do not resemble visa exempt abuse or back to back border runs. What would matter in practice is your prior entry history to Thailand. If you do not have a recent pattern of long or repeated stays, a third entry should not be an issue. As long as you have onward tickets, accommodation details, and can show that you are genuinely leaving Thailand between entries, this should be well within what is normally accepted. Entry is always discretionary, but nothing you’ve described would usually raise red flags.

Yes