The discussion is wrt bearing failures in AHU blowers.
Earlier, these blowers were motor driven at constant speed and pressure control by the means of inlet guide vanes. The AHU arrangement was as follows: Prefilter, air filters (10 micron), air Filter (5 micron), Blower, Cooling coil (to cool air from 30 degC to 15 degC), steam coil and humidifier to adjust as per exact process requirement.
Later on, the blowers were made VFD driven and arrangement of AHU is changed as follows: Prefilter, Air washer, Cooling coil (to cool air from 30 degC to 15 degC), steam coil, Blower, Fliter (5 micron) and humidifier.

Simply speaking, as per original installation, blowers wers operating at -40 mmWC g, 30 degC and 60% RH. While as of now blowers are operating at -100 mmWCg, 15 degC and fully saturated air.

These are critical equipment and many such AHU are running. In some of the AHUs we are getting frequent bearing failure. Our CM dept is capable enough of identifying failure mode, condition monitoring etc. Bearing failures were largely attributed to fatigue, electrostatic charge on blower due to condensate carryover, misallignment etc.
But still there are weird failure patterns. Bearings in some AHU are only failing repeatedly and not in ALL AHU. in two AHUs we got bearing life of only 1 month.
Blower specs: air flow: 20000 CFM at 310 mmWC diff pressure.

Does anybody have any similar experience?

Have you actually gotten an experienced RCFA person to analyze the failed bearings in an attempt to determine the cause of such frequent failures.

It is extremely difficult to compare or make any kind of guess, whether one has similar failures or not. Each case is more than likely unique in its own right and would need to be examined individually.

Are the "attributed" causes you listed, different from the "weird failure patterns" you refer to?

Only my opinion and I might be totally wrong.