Yeah this happened to me but it wasn't after a contact experience exactly, it was after a particularly intense remote viewing session where I picked up something that genuinely scared me. Started seeing 11:11 and 3:33 constantly for about three weeks after. Like annoyingly constantly, not just "oh I happened to glance at my phone" - I mean waking up at those times, receipts, random page numbers, the lot.
I don't know if its the brain doing something weird after a psychically stressful event, like it's pattern-matching on overdrive, or if something external is actually trying to communicate. Both explanations feel uncomfortable to me for different reasons.
What I will say is the numbers stopped when I started doing proper grounding exercises after sessions. Make of that what you will. Anyone else noticed whether it fades on its own or only when you actively do something to close off? Genuinely curious whether there's a pattern across different people's experiences.