The length of a particular disc could be the problem. A check-up/diagnostic couldn't/wouldn't hurt.
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If your handy and want to save some $$
1st, try cleaning the lens, slide rails, gears, then lube (with the proper lube, sparingly)
2nd, try having the lens adjusted (good local tech did mine in 5 minutes)
3rd, if all the above fail, replace the lens and you're good to go, as long as the servo(s) are in good order.
I replaced the lens (Samsung) on my CEC and had my local tech dial it in, works better than the day I bought it.