Concentrated stock solutions like 10x TBE buffer can form a crystalline precipitate over time or in colder conditions. This is entirely normal and does not affect the composition of the buffer chemicals. Cloudiness or a few small crystals will disappear when diluted to 0.5x or 1x working concentrations.
To remove heavy crystalisation, heat the 10x TBE buffer at 40°C–60°C until the crystals redissolve. Very heavy crystallisation may require increased temperatures or increased time to redissolve.
If your 10x TBE buffer is in a 50 mL tube, add hot water to a beaker, and place your 50 mL tube in the beaker until the crystals dissolve. Occasional shaking of the tube can speed up crystal dissolution. Alternatively, pour out the 10x TBE buffer and crystals into an empty beaker, microwave it in 30 s blasts until the crystals dissolve, and pour it back in after cooling.
If you have a 1 L bottle of 10x TBE, transfer all liquids and crystals into beakers and carefully microwave in short (e.g. 30 s) bursts until the buffer is hot. Gently swirl until the crystals dissolve (this may take some time for heavy crystallisation).