"Is investing in a syndication risky if the market changes? I don't want to invest money for years in an apartment deal if there is a chance the market could change and leave the syndicator broke. Any suggestions on this?"
There is definitely risk. That is why all PPMs say the investor should be prepared to lose all their principal before signing.
I am sure you know we are in the late stage of the RE cycle. The economy is arguably overdue for a correction. While multi-res was found relatively recession resistant during the last great recession, it does not mean it will be the case the next time given all the building that has been going on. While homeownership is still a challenge for many, I can also see that in the next downturn, because of the recent increases in rents, renters may start doubling up and sharing rooms.
If rents dropped enough or vacancies rose enough so than the property's income could not service the debt, the lender could call for repayment and that would be the beginning of the end for the investors investment.
My suggestion at this point in the cycle is to find sponsors that have been through the last recession and projects that are conservatively leveraged. Less leverage usually implies lower returns but it also provides a greater margin against market forces, the impact of which the even best sponsors may be challenged to navigate through.