Some Search Keywords Not Hightlighting

Hi,
I’m using WPSOLR plugin but I’m facing one problem with hightlight.

Issue:

Some search keywords are highlighting and some keywords are not highlighting.

Please refer the issue in demo site also
https://www.gotosolr.com/search-results/?search=especially
Here, search keyword is “especially” it displaying some results but no highlight in the search results.

Kindly check and do needful to fix this issue.
Looking forward to hear from you!

https://www.ads-software.com/plugins/wpsolr-search-engine/