Without any real facts, I would like to say, that it is not true.
When you buy them as a componenet, they come in a bag and there is no possibility at all to check how they are placed in the bag or under shipping.
All I know is that they can dry out if they are mounted, used or left for too long and exposed to high heat.
Possibly they can freeze.
Or possibly they could be exposed to pressure changes under the flight if the shipping space does not have pressure equalization, which could causes them to contract and expand.
If this could harm them, I do not know.
But none of the above is affected by, if they are standing or lying down.
We have many frequency converters and soft starters at the factory that are sent for repair and come back both new and repaired.
And we have no idea how they are transported.
And I have never heard of anyone not working.
Mayby I should have asked if you are refering to the condencators or the cabinets lying down ?
In this picture, the capacitors are standing, but when they are mounted in the cabinet, they are horizontal?
Best Regards A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein