If this is a one-off, then I recommend;
#1 - Rechecking the interior to ensure that there is nothing blocking the slides such as an open cabinet door, couch out of position, etc. It appears to me, based on the sketch above, that you can be inside to watch the unit closing up. the smallest of obstructions can cause the biggest headache. Be certain to check the top of the slides too!
#2 - Checking the fluid level for the hydraulic pump and then then cycling the slides. It could be a low fluid issue or debris in the lines.
If this is a consistent problem from the first day of ownership, then there is an adjustment underneath as suggested by mikendebbie. I, too, doubt this is the problem since both slides have this issue.
This is an interesting problem, and I would be curious to know the cause.