Is there any rule or guidance that prevents the Reserve Component from issuing consecutive Monday-Friday orders?

This has happened multiple times to my National Guard unit so I'm very curious to hear what input others can provide, I wasn't on the orders for this time but I know multiple others in my unit got screwed on their benefits & BAH because of this.

Frankly, it depends.
If these are orders for "unit support", then the SM would be on a M-F schedule minus holidays, just like the rest of the full-time unit support. It makes no sense to pay individuals when they are not working, nor to bring in FTUS personnel on the weekends just to provide guidance and supervision to the guy on AT/ ADT orders. FRAG AT is a common way to pay in these situations.
For longer tours that involve a special project, orders over 30 days should be on ADOS (special project), CO-ADOS (deployment, pre-deployment, or post-deployment support), or ADT (shorter-term special project or operational sustainment ie a CTC). Those orders should run as a standard block of 30-365 days and any off time be prescribed by the commander.
Rules governing this will be in the pay and training guidance, usually put in place by the MACOM (GO Command) level HQ.

I've had this happen many of times in units I was attending often the reality of the situation is there is only funding available for limited orders often 14 days or less. There simply isn't authority for a longer term order. But also these orders are strictly voluntary for anything over your standard AT orders. You loose pay and all benefits like healthcare, and leave. But for many Soldier's it's better than where they were before.