Repair that grout joint, and all you've done is set it up to crack again. Most likely, the reason that particular joint is cracking is because that's where the top of the pan membrane is. Most likely, it's time to replace the shower pan, as well as about 18"- 2 feet up the walls. One thing everyone who reads this thread needs to keep in mind-- when grout cracks, it's not the problem. It's a SYMPTOM of the problem, and 9 times out of 10, that problem is either structural movement, or moisture getting at the framing and making it swell. Either way, the problem needs to be identified and mitigated. Otherwise, you can grout it, caulk it, tape it up-- whatever. You're still going to have a problem that will need attention sooner or later, and the sooner you take care of it, the cheaper it'll be to do so.

I also agree about elevating the older dog to a dominant position in the house. When our dog died, and we brought in a new companion for Ricky, we intentionally always went to Ricky first, and said so. Ricky, let's go outside. Our pup learned to "wait for Ricky" as he would walk proudly out the door first. When we fed them, we would say Ricky eats first. Actually we only set down his bowl first, then fed the pup. Even now a year later, we always let Ricky go first and make a big deal of it. Blaze knows nothing else. Ricky leaves and enters the house first. He eats first and gets in and out of the van first. We brush him first and pet him first. Even if Blaze runs up to us to the gate first, we often will stop petting him and pet Ricky when he arrives. All of our dogs are lap dogs. We just sit on the floor. In time when the older one feels more comfortable, the little dog may be a more exclusive lap dog, but for now, I would sit on the floor, and pet the older one first. We keep our dogs in the most popular area of our house, so we go to them. They are rarely alone, but we do not allow them into our living room or bedrooms. Those are off limits, so we don't have dogs with us 24 hours, and we sleep without dog dander since we are very allergic. Therefore we can easily declare that Ricky is first in whatever we do. I don't think you will have a problem after a couple of weeks. If you do, you might consider discussing this with the Vet to see if there is a mild medication you can give your older dog for anxiety. One more thing - when we were walking our dogs, Ricky used to always poop. We would scoop it up, and walk with it. Once my husband hurt his back and had to stop walking with us for a couple of weeks, I quickly got tired of this process. Before our walks I would take the dogs out as usual, and I began telling Ricky to do his business. He would walk inside, and I would call him out. I kept telling him to do his business, and he began doing it. Now he understand that he must do it before we walk. We haven't needed the bags for about 6 weeks. It may be that your dog is performing for you in a more dramatic fashion than the pup can do. You might keep the dog outside with you (and not the young dog), and insist that he poops before he comes in. Even give him a treat if he performs for you. We all know that a dog's brain is wired completely different from ours. Sammy

It is normal to see spider crazing, and they will disapear as soon as the area becomes hydrated.There is no need to "call them back asap"

If you have a curb, you will have the cracks develop there, too. and where the walls meet the floor. Anywhere where two different materials meet or where one surface meets another that is in a different direction (known as "change of plane"). My contractor still grouts such places, too. But I did a solid surface shower that he could not do wrong. I am keeping an eye on the place where the floor meets the shower pan, all other places are in dry areas. So there it is just cosmetic. I would guess that water can get behind your tile with those cracks. If properly waterproofed it is fine, but if not, I would get to this as soon as you can. A lot of shower builders do not use waterproofing, even though it is now required. If you do a search on this forum for "Shower waterproof," you can see many discussions about it and learn what is and is not waterproof. (Redguard yes, Durock no, for instance.)