Hello Orga78,
I see now the connection with your thread408-428919.
With your post above describing incidents 'days apart' you have either (if this is different, but similar position for more than one valve) a systematic failure after x hours in process, or (if repeated for one valve after repair) already weakened components not changed, contributing to new failure.
The cause of failure for ball-valves with actuators, not including failures of the actuators itself, is most often wear of sealing, often given by extreme fluid conditions with abrasive actions and deposits.
A 'normal' failure sequence is, depending on application, somewhere between three months and factory's lifetime, average perhaps 1-3 years up to 10-25 years.
Both type of repeated failures will show you nothing but weak, not correctly selected and/or supported equipment for your purpose. 'Tilted stem' may be caused by heavy weight, but also tells you that some of the stem construction or bearing is too weak.
Sidewise mounting can contribute to abrasive wear of sealings/bearings for the stem.
Check that the ballvalve you use have solid stem bearing, solid stem, supported with bearings top and bottom, extra sealing rings to prevent fluid reaching the stem bearings etc. In addition check that the supplier says OK to sidewise mounting, preferably with references,and this in addition to aligned support for pipeline, valve and actuator.
Note: a too stiff connection between actuator and valve, can give stem and bearing/sealing damage if unlinear forces occur.