This is accurate. Had a friend fly into Doha on Friday evening about 19:00 only to be denied entry. She has worked here in the last two years, and apparently from the 26th of September new laws are in place that if you have held an RP in the last two years you need some documentation to enter the country on a tourist visa. It is some sort of letter from your previous sponsor saying that they don’t object to you returning and that they take responsibility for you, etc, etc.

See quote below from the British Foreign Office:

As of 26 September, we have been made aware of new immigration regulations that may affect British passport holders that have previously held residence permits in Qatar. We strongly advise all British nationals that previously have held residence permits in Qatar and are planning to travel here as tourists to contact their airline or nearest Qatari Embassy to check the immigration requirements, as it may not be possible for them to purchase visit visas on arrival at Doha." http://www.fco.gov.uk/en/travelling-and-living-overseas/travel-advice-by...
My friend was able to contact her previous employer and a clerk ran around to various iftar dinners and got the letters and she was granted entry at about 02:00. The details of exactly how this letter needs to be worded are unclear, but you can re-enter with permission of your previous visa sponsor, if they are willing to grant it.