If an EB-5 investor need to travel overseas, is the six-month rule considered in the aggregate or in a row to not risk losing my visa?

Two considerations: eligibility for citizenship and abandonment of the green card. Eligibility for citizenship is based mostly on fixed rules; no breaks greater than 180 days out of the U.S., continuous residence in the U.S. for at least half of the five-year statutory period, and residence in the state for 90 days before filing. For abandonment of the U.S., it is more of a factual test of intent; are you paying U.S. taxes, were the breaks greater than a year, are you employed abroad, what are your ties to the U.S. If extended absences are anticipated and/or employment abroad, I recommend applying for a reentry permit while on U.S. soil but still keep up U.S. tax payments on worldwide income as well as other ties to the U.S. to show your intent not to abandon the green card you worked so hard for.

If you plan to stay outside of the U.S. for more than 180 continuous days, then a reentry permit may be helpful. If you are making frequent trips back and forth, it may not be necessary. The frequent trips and the total time spent in the U.S. versus outside will make a difference in when you can apply for naturalization/citizenship (you need to be in more than out over the 5-year period before filing).

As a lawful permanent resident (whether or not a conditional one), you must maintain the intention to permanently reside in the United States. An extended absence, say of more than six months on any given trip, would raise a rebuttal presumption that you no longer maintain the required intention to permanently reside in the United States. You can rebut, or overcome, that presumption by showing your intention was not to abandon your permanent residence, that your trip abroad was necessary, albeit prolonged, and that you still have ties to the United States such as property ownership, employment/school records, resident tax returns, bank statements, medical records, insurance, utility bills, etc. If, for example, you departed the United States and were absent for only five months, then returned for one week, only to depart again for another five months and repeat only spending one or two weeks in the United States, eventually the CBP will begin to question your intention, i.e., whether you really intend to permanently reside here. If you need to spend significant time outside of the United States, it is recommended that you apply for a reentry permit (on Form I-131) prior to your next U.S. departure. With a reentry permit, you can remain outside of the United States for up to two years without abandoning your green card. The same is true for your spouse and any dependents who are U.S. permanent residents.

There is no six-month rule. If you have a green card, you are expected to live in the U.S., but can be out for up to 6 months without breaking the continuity of your resident status. At all times, you must file tax returns and maintain your ties to the U.S. To hold a green card, this must be your home, but you can spend time abroad provided you intend to return to the U.S. as your home, always.

You can travel as long as ideally you are not outside the U.S. for more than 179 days at a time. Worst case you should not be outside U.S. more than 364 days a time. It applies to your spouse if she is also a permanent resident.