Pillow block bearings are very tricky to lubricate. They require a layer of lubrication under 1/1000" thick. If you fill some, most or all the space with grease, the small rollers have to push the grease out of the way with every revolution and this creates heat and lubrication failure. Many pillow block bearings can use oil. With the heat, the expansion of the grease pushes on the seals and causes a failure.
When you have failure, can you see the rollers? Are they dark colored from the heat? When the saw is stopped, can you feel heat on the bearing housing?
Also, when the grease cools at night, this creates a vacuum that sucks in contamination...the hotter the bearing, the greater the vacuum, so the more dirt.
I suspect your rpms are low, so you certainly do not need grease, very little each time-one small squirt-, more than every month or two. If you see grease leaking out the seals, you have many times more grease than you need. A properly maintain pillow block bearing will outlast the equipment.
The #1 cause of pillow block failure (50%) is over greasing. Your comments indicate over greasing. The #2 is poor alignment.