The first thing I would check is the gas syetm. The Mini-14 has an operating rod that slides over the gas tube as it's going into battery. Just before the bolt closes all of the way, the gas "plug" slides into the hole/port at the front of the rod. (Charging handle rod) I would check that for damage or crud buildup.
To eliminate any issues with the trigger unit, as soon as it locks up, remove the trigger unit. If that frees it up, look there for problems. You can also narrow down the problem by checking if the operating rod/charging handle has any forward and/or rearward play. In other words: If the bolt is locked up for some reason, you will be able to move the charging handle forward/rearward a small amount. If the charging handle is solid with no forward/rearward movement, see the first part of this post. Keep yer powder dry, Mac.
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