If the clips are on track 1, switch to Storyboard mode and verify that there is no gap between them. If there is, right-click in that gap and Close Gap.
A crossfade between the clips should work if the clip lengths are long enough to accommodate the fade.
If the FROM clip has no excess video after its end point and the TO clip has none prior to its in point, then there's no video to accommodate the fade. The result will be a freeze. To counter that, go to OPTIONS | EDITING tab and for the transition choice choose Ask Me. You should then see this pop up when applying the fade...

Choose Overlap. Be aware that this can throw audio out of sync if the audio track isn't linked to video.
If this doesn't explain the issue, share the project so it can be analyzed. Mention specifically how the crossfade has been applied,
The process is easy, quick and can be done privately. Just follow these steps closely...
Back up --- With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
Upload --- Use a free server - Google Drive, MS OneDrive, etc.* - to upload the saved, numbered FOLDER. Do NOT upload the individual VPJ or export file.
Get link --- Get a public link. Right-click the file and click SHARE. When using Google Drive, if necessary change "restricted" to "anyone with the link can view"
Share --- Click COPY LINK | DONE. Paste that link here, or click the folder at the top-right of this forum to message it privately to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.