As long as there are no indicators of seasons, your plants are on the seasons you dictate. Do you have your plants on timers and are your plants protected from any other lights to include daylight through the windows? !8/6 is great for young plants and vigorous growth. That season is late spring early summer. The tomatoes and Cosmos need some tweaking. Lower nitrogen in proportion to the phosphorus and potassium. Reduced fertilizer application. And gradually reducing the daylight hours versus dark hours to 12/12. This replicates going from summer to late summer to fall and promotes flowers/fruits.
The other plants are leafy greens, chives, basil, mint, sage (grown for vegetation not flowers and fruit). They do best with Nitrogen equal to Phosphorus and Potassium. They will do fine even at 12/12 for the tomatoes.
Cosmos are an annual and will be happy with low nitrogen the entire growth and flowering period. Too high nitrogen and you'll get lots of Cosmos leaves tiny buds few if any flowers.
What are you using for fertilizer? Twice per month? How do you water? Is your grow room completely protected from light outside the grow room? Just a little light or peekaboos will confuse your plants. What soil are you using? Plants rely on stability. If their environment is not stable (getting 18 hours of light and 6 hours of dark...changing to 12/12...then all of a sudden getting bright light during the middle of their dark cycle that is one instance of instability, change in temperatures and daily temperature differences...) As long as your plants get stability in everything, they'll be happy. What are you using for soil? What kind of lights are you using? Are you able to keep temperatures no lower than...55F and no higher than 80F? Are you using fans? Do you have a way to pull fresh air in and push old air out of the space? The more artificial your garden the more input you will have. Less margin for error.
You just have to send a picture or a bit more information on your plants, garden and maintenance practices. What fertilizer you are using and what kind of soil? How do you know when to water? Your plants are very different in their needs. How old are your plants? How long have you been growing your plants? A few of your plants are annuals, a few are perennials, a few are woody perennials...all with different needs. Are you able to make two rooms out of the one?