The preferred dividend must be paid in full before the first penny is distributed to common shareholders in dividends. Basically, as long as the reit does not go bankrupt your dividend will not change and will be paid out.
Wrong; they can suspend the dividend, even if they do not go bankrupt. The suspension could last several quarters, and if they resume paying a div, all missed divs would be paid since this pref is cumulative. However, it is erroneous to assume the div must be paid out on the scheduled dates.