It’s normal thing most of us experience. I’ve read a few more recent studies about it, but afaik there is no certaon explanaition yet. Here’s an excerpt from wikipedia describing it:
“A study by Chris Moulin of Leeds University asked 92 volunteers to write out “door” 30 times in 60 seconds. In July 2006 at the 4th International Conference on Memory in Sydney he reported that 68 percent of volunteers showed symptoms of jamais vu, such as beginning to doubt that “door” was a real word. Moulin believes that a similar brain fatigue underlies some symptoms of schizophrenia and Capgras delusion. Moulin suggests that people with these conditions could be suffering from chronic jamais vu.[1]” en.m.wikipedia.org/wiki/Jamais_vu