Thrust spacers not ...

Thrust spacers not installed, probably also no permeate tube interconnector shims, or thrust cone not installed.  Or these could have been installed on the wrong end of the vessel, making them useless.  8" diameter membranes as yours appear to be, the thrust from 40 psid would be ~2000 pound force.  That might not be enough to telescope the membranes, however, if the thrust increases to something like 3000-3500 pound force without support, you can kiss them good bye.

70 psid would be way outside the normal operating envelope of clean membranes being operated at the correct feed and cross-flow, therefore there are several mistakes being promulgated in your system.  Operating on staged system with seawater cannot be good because of the high osmotic pressures in the second stage, and also higher recovery means much higher particle loading on surfaces and leaf spacers within each element, resulting in high differential pressure out of range.

That is, unless there is some sort of miracle filter upstream of the RO.  I still do not like your system design, and I surely do not approve of the way these membranes were installed even if the design had been passable as stable.

If you want a zero-discharge seawater RO system/hybrid system, you will have to do much better.

Consider backing up to the design point.  Consider PFRO, where the brine discharge is closed for some part of the operating cycle, then cycled open briefly, with all vessels operating as first stage. The brine that is discharged will be under higher velocity, thereby cleaning off more particles, and the system will operate with lower particle fouling at the active surface, and lower concentration profiles at the surface for most of the "duty-cycle".  You will need to consider carefully the hydraulic characteristics of your system during brine discharge step, so as not to over stress the membranes with thrust.  The brine will be then heat treated to crystallize out the unstable minerals in a crystallizer.  The crystals may be marketable as animal feed supplements, perhaps.

The brine from the crystallizer is then fed back to the feed makeup tank/blending tank, and a small portion is discharged prior to back-blending, due to high salinity, but only the amount to be handled in a salt crystallizer process, where even such things as magnesium, and Lithium salts can be won, as well as the usual sodium chloride.  In the end, nothing goes back into the sea or ocean, and you have done your environment a huge favor.