Heroku Error Compiling CSS Asset - css

Question

In my latest deploy to Heroku I'm getting this error:
Error compiling css asset
Rack:Timeout:RequestTimeoutException: Request waited 3ms, then ran for longer than 1500ms
/app/vendors/bundle/ruby/2.20/gems-sass-3.4.22/lib/sass/tree/visitors/to_css.rba;67:in 'erase!"
I'm not quite sure what has caused the issue, but I've narrowed it down to a specific deploy where things were working before but were broken after. The only thing I changed were html files and changed the value of a sass variable in one of the stylesheets. I committed to git then deployed to Heroku. I realized then that my jQuery wasn't working on the page, so I then precompiled locally (as I usually do) and deployed . Now the application is throwing that error and exceeding it's available memory. Yet, everything works just fine in development. Anyone have any idea of what went wrong?
EDIT: I should add that the Rack timeout error is thrown by the rack-timeout gem which is designed to stop slow requests and log an error. So this isn't directly the issue, rather a result of an underlying problem that's prevented the page from responding within the allocated amount of time.
Here's the gemfile as requested:
#Use Jasny Bootstrap extension for input mask
gem 'jasny-bootstrap-rails'
#Use for Blog tags
gem 'acts-as-taggable-on', '~> 3.4'
#Use Carrierwave for image upload, fog for AWS S3
gem 'carrierwave'
gem "fog-aws"
gem "mini_magick"
# Use bootstrap will-paginate for pagination styling
gem 'will_paginate-bootstrap'
#Use will paginate for pagination
gem 'will_paginate', '~> 3.1'
#Use BetterLorem for seed text
gem 'betterlorem', '~> 0.1.2'
# Use date_validator gem to validate Event start & end times
gem 'date_validator', '~> 0.9.0'
# Use Bcrpyt for password encryption
gem 'bcrypt', '~> 3.1', '>= 3.1.11'
#Use FontAwesome for icons
gem "font-awesome-rails"
# Use to obfuscate email addresses on site
gem 'actionview-encoded_mail_to', '~> 1.0', '>= 1.0.7'
# Use to show instagram feed
gem 'instagram', '~> 1.1', '>= 1.1.6'
#Use TinyMCE to edit html content in posts
gem 'tinymce-rails'
# Use Jquery-turbolinks to fix turbolink issue
gem 'jquery-turbolinks'
# Timesout request that take longer than 15 seconds
gem "rack-timeout"
#Breadcrumb navigation
gem "breadcrumbs_on_rails"
# Use Gibbon for Mailchimp API navigation
gem 'gibbon', '~> 2.2', '>= 2.2.4'
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug'
gem 'pry', '~> 0.10.3'
# Use sqlite3 as the database for Active Record
gem 'sqlite3', '~> 1.3', '>= 1.3.11'
# Use for storing environmental variables
gem 'dotenv-rails'
end
group :development do
# Access an IRB console on exception pages or by using <%= console %> in views
gem 'web-console', '~> 2.0'
# Tracks memory usage of each gem
gem 'derailed'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
end
group :test do
gem 'minitest', '~> 5.8', '>= 5.8.4'
gem 'mini_backtrace', '~> 0.1.3'
gem 'guard-minitest', '~> 2.4', '>= 2.4.4'
gem 'guard'
gem 'minitest-reporters', '~> 1.1', '>= 1.1.8'
end
group :production do
gem 'pg', '~> 0.18.4'
gem 'rails_12factor', '~> 0.0.3'
gem 'puma'
end