Reason for elevated pH
What is the pH value the rest of the day?
Is there any water contaminated by a chemical substance, such as a lubricant or hygiene product, etc., that could possibly be overflowing?
What are your company's activities between 6am and 6pm and conversely between 6pm and 6am?
The first idea that comes to mind is that you may be cleaning floors with a highly basic product. But other hypotheses are possible.
Do you perform any mechanical cutting that would require machine lubricants?
If the answer is yes, check your safety data sheets; this should give you the product's pH value.
Another avenue to explore, already mentioned in the two previous comments, is the use of detergents either for floors or used in batch washers.
Here again, check the safety data sheet for pH levels.