Lemond Chambery/Cannondale R-900/Trek 8000 MTB/Burley Duet tandem
ANy rim, any count needs to be retensioned after about 200-300 miles. Spokes seat, nipple turn, spokes break in whater happens, the wheel loses tension. Needs to be retensioned or it will allow movement along the hub flanges resulting in broken spokes. Wheel is moving like silly cause not enough tension.
If it's new, take it back to the shop for the free tuneup. Tell them to retension the spokes. If they true it without retensioning, then the mechanic sucks! Needs tension! If he says he retensioned then spokes start to break, then the mechanic still sucks............Means he bound and twisted the spokes.
You don't mention what wheel setup it is. 24 spoke? 32 spoke? Either way, low count spoke wheels don't usually last a big guy but maybe one year, if he rides app. 4,000 a year