Can anyone help me to identify what is wrong with my Muscat Vine?
You might want to consider the Ontario IPM sheet related to Nitrogen deficiency. In particular this mentions that cool weather or very dry conditions can cause the vines to fail to benefit from N in the soil. The N is there so there is no need to increase levels, just wait for conditions to change. The yellowing of leaves, with red in the petioles and shoots as indicated in your image would be consistent with low N. Clearly your plants are quite advanced for the season compared to Ontario, so perhaps you are in a favourable climate or greenhouse situation?