TLC can often be far more sensitive than certain forms of NMR, particularly if using a lower field stength (i.e below 400 mhz for proton for example.) To determine if the compound is degrading on the TLC plate. Perform a 2D TLC. Run the plate in one direction and then turn the plate 90 degress and run in the new direction. If the spots do not fall on or close to the diagonal line created by the two starting lines, then they are changing as they move along the plate.

Another option is to spot the compound, wait an hour and spot it separately next to the first spot, then run tlc and see if there is decomposition with time. If so, you can always buffer flash silica with 10 mL pH 7 buffer per 100 g of silica - turn slowly in RB flask on rotavap overnight, no vacuum, to enable column chromatography without degradation.