Here are a few possible areas that you might look into:
- weak oprod spring (find another Garand that functions properly and compare the effort it takes to pull back the oprod)
- Google for Garand "short-stroking"
- take your rifle apart, clean and re-lube according to Garand specs (grease in the proper areas)
- while your rifle is apart, look for any burs or rough spots that may inhibit the oprod fro functioning properly

If you have to bump the oprod to get the first round to chamber, the friction of the rounds in the clip might still be enough to keep the oprod from stripping off the second round if the spring is weak.

Tom