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.

I can't answer for the rules. They'd always decide on what isn't most beneficial to the Air Force. However, if you are a commuter they shouldn't be cutting Monday-Friday orders. So live somewhere about 3 hrs away from you really duty location and you should be good.

If it is at, orders over a weekend should only be on working weekends. If you're on 30+ day orders for backfill support or schools it should be consecutive.

I am not sure of the exact policy/guidance, yet I will add that if the member is not local, the Unit will pay for each round trip to/from the Unit... AND, the wear and tear of the member schlepping back and forth... AND the lack of benefits.

Sadly, I am pretty sure it is legal, yet highly questionable to the welfare of the member. Yes I know, mission first, yet member has bills to pay.

If there are Monday to Friday orders there may not be a consistency. If it is during an Operation. The Member will not get credit for the Operation or lose points and pay.

If its for longer than 30 days then yes that is pretty jacked up. The SM then forfeits full benefits. They usually do this at home station because no one works on weekends so they don't want to pay soldiers for two days to stay at home. The only other reason would be because they may use different fund managers to pay these orders. So they may use a Soldier's AT days first, then switch to ADT, and then utilize ADOS and such. This would mean they would all be on different sets of orders. ADT orders longer than 5 days require Tour of Duty requests. And that requires higher approval so Units try to avoid that. To my knowledge there is no regulation that states you would have to do M-F in any circumstance in regards to extended orders.

I have never seen this, but if so they are not looking out for the well fare of their troops.