There are lots of causes for variegation in cannabis- genetics, poor feeding habits, root issues, etc. HLVd is a fairly obscure disease that affects hops and cannabis that honestly I wasn't even aware of until I began working in the cannabis industry. It's a sneaky virus that doesn't usually let its presence known right away. When it starts presenting it may appear that the plant is just growing a little slowly but soon the branches begin to become very brittle and will branch weirdly. Usually they'll grow sideways because they can't support their own weight and you might think it's a root rot issue. Chlorosis will eventually set in and leaves will start looking malformed. If taken all the way through flower it GREATLY reduces trichome quality and potency. A strain that should test in the mid 20s might be like 8% lol. Thankfully, this problem is mostly limited to your large scale grows. The most common way a hobbiest grower is gonna encounter it is buying infected clones. Some studies are considering the possibility of it carrying over to seed but as far as we currently know it's mostly transmitted via dirty tools/environments once contaminated. Bleach will kill it at a strong enough concentration but once a plant has it you should probably kill it off- there's no "cure".