The trigger definitely does not have the original sealer on the screws and has been adjusted.
Nothing wrong with an experienced person skillfully adjusting a REM trigger. But, neglecting a stock box trigger is bad, and worse is to neglect a lightened box trigger.
Every season, remove the barreled action from the stock, and while inspecting the trigger, hose it down and flush it out with a bottle of Ronson lighter fluid. This will keep it clean and leave just enough lubrication to keep the trigger running trouble free. If neglected, debris and the various solvents and oils used on the rifle will creep into the trigger, and will gum the works over time, which can lead to the issues you describe. A trigger set on the light end will hang up quicker than one set on the heavier end.
If neglected badly enough so that a varnish has built up, or the wrong product, such as an alox, was applied, you may need to remove the trigger and soak in a solvent to remove the varnish. Once clean, lightly lubed with the residual of the Ronson, properly adjusted, and with the yearly inspection and cleaning; it should run for quite some time before physically wearing out.
Best
