Honey Oat Sourdough Slow Rise

Toast

if I mix a normal sourdough and a honey oat side by side the honey oat takes about 30% longer to rise. 

 

Anyone know why?

 

Fyi I do a 65% hydration 2% salt and 1:3 ratio starter to flour. I usually add 50 grams of honey per 500 gram loaf. Then I'll top it with oats. 

Honey has antibacterial properties, so depending on the amount it could slow down fermentation.

Ingredients used to enrich doughs I.e sugar, honey, dairy and fats naturally slow down fermentation for reasons I don't know. If you really want to speed up rising times on your honey oat loaf maybe add a small amount of dried osmotolerant yeast to your recipe maybe 0.5% of yeast to flour weight along with your levain. This yeast performs well in high sugar conditions

Thank you all so much for your suggestions. I'm glad I'm nit the only one to run into this problem.