I was cutting firewood (large white ash) and the chain would occasionally not move after a cut. I would drive the bar down against a stump edge to free it up. After a while even that wouldn't help. The saw (Redmax GZ500) is less than a year old - small and light for this arthritic 71 year old.
The bar tip sprocket barely turned with a screwdriver and hammer tapping the teeth around. PB Blaster, WD 40, and even a stiff wire through the backside of the sprocket brought no cure. Finally, I tapped the tip with a ball peen hammer with some force and the tip sprocket freed up. I've always greased the tip and this bar (and saw) is less than 1 year old with maybe 4 cords of firewood on it. Any ideas what happened?
I've seen tips/chain stick when cutting with the tip in the cut or partially in and the log kerf closes up some, what was happening is the saw dust can't clear and gets jammed in the bar at the tip. If I see it happening (chain slowing down and kerf closing up) I will remove the saw from the cut while keeping the chain turning to clear the jam, if you stop turning the chain it will get stuck.
Also, especially with ash, the sawdust will pack in and stop the chain. Just dragging it backwards usually frees the chain and the clog. But also as Hilltop366 has found, works for me.
I will check the bar and tip with each change and or sharpening of a chain. I clean the groove, and if the tip does not spin, add some of the above or blue creeper, and spin it with an air blow gun. when it spins like a turbo, you are done. I then add some light oil and replace the chain and back to work.
Every time I've greased my bar tips, the tip blew out shortly after. I threw my little grease gun out in the woods.
To expand on my post a bit.
What I figure is going on when the kerf closes a bit it naturally closes more at the top of the bar than the bottom and because of this the chain at the top of the bar is cutting the sides of the kerf making short fine chips and at the same time the chain is rising out of the bar grove at the tip because of the closing kerf holding up the chain. With all of the conditions lined up it lets the saw dust go under the chain and enter the bar grove and get pushed in further by the drive links.
I never grease a bar tip. just not necessary. Keep your oil pump turned up all the way, keep your bars filed smooth and keep them ridges and burs off, keep your chain tension right and your bar tips will last quite a while. I rarely replace a tip.
You might try soaking the bar tip in a coffee can filled with kerosene then flipping the bar .Might blow it out ,might not .
With ash, it is probably getting sawdust under the chain and packing into the tip. I'm not sure what you can do other than turn your oiler up, and revving the saw every now and again out of the cut to help clear it out.
All the ash with few exceptions has been dead for about ten years and is dry as a bone and hard as rock .It blows a lot of powder and dulls chains rather quickly .You might try using the file more often than normal .I've had some it's a file about every tank of fuel .