What are the common bugs to occur during website design?

What are the common bugs to occur during website design?

bugs are the errors which may occur due to many following reasons
yes of bugs are:
Design, functionality, spelling, compatibility, usability, and security.

Among may bugs, few are the below bugs

Bug Severity
Bugs by Browser
Bugs by mobile device

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Improper input validation
Improper escaping of output or encoding
SQL injection
Cross-site scripting
Race conditions

Some of the common bugs which may occur are :

Functional bugs: These bugs arise due to break in functionality of the application or if some module of the application is not working as per expected behavior. The most common functional bugs in any application are incorrect validation, no validations, buttons not working, unable to login/change password etc.

Corner/Unlikely bugs: These are most rare use cases that might be executed by end users like saving the user name with special characters, creating new user with name having white space as a prefixes etc. Mostly, these are low priority bugs which do not gains much votes for their fixes during bug triage.

Cosmetic/UI bugs: These are the issues that are more likely to be occur in all software applications. Although these issues does not have any impact on the working of the application, but has lot on look & feel side of the application. Most common types of UI bugs are misaligned fields/images, truncated text, color validations, typos, font size of texts and many more like this.

Blocker/showstoppers bugs: These are the bugs which occurs when positive tests get failed which further blocks other modules of the application and thus gaining the attention of development and product management teams. Also, these bugs can impact the release of the application if not fixed timely. Few examples are unable to login into application, application crashes while navigating to different page & unable to reset password from login page.

Also few less common "bugs" would be poorly designed input forms, inefficient usage of responsive design and javascript functionality with no fallback.

Bug Severity
Bugs by Browser
Bugs by mobile device

Most common bugs are:
Browser compatibility issues
Responsive website mistakes
broken links
slow site speed