I installed 8 SXT LTEs around 18 months ago. 3 have died in the past two weeks - all R11e-LTE card failures.
They are all connected to an HAP AC Lite using PoE and the provided PSU.
Is there anything I can do to avoid further problems, or should I expect to replace the cards regularly?
you can and should write about every that case to support@mikrotik.com - they can do change and discovery why that card is damaged.
All LTE devices are warranty fix via MikroTik directly and give that wrong cart to warranty. They should be stable.
I remember old post about the waterproof of sxtr.. http://forum.mikrotik.com/t/sxt-are-not-for-outdoor-damaged-units/61331/14 AND http://forum.mikrotik.com/t/mikrotik-routerboard-sxt-5d-16db-antenna-weather-concern/44629/44
example normis say it’s outdoor device in http://forum.mikrotik.com/t/is-the-mikrotik-sxt-lte-kit-rbsxtr-r11e-lte-waterproof/122027/2
But when you must use 2x ethernet and groud cable then you have problem and must do cutting in plastic cover…
if you not give feedback then nothing will change, write with picrutes/logs/story etc to support@mikrotik.com