Issue Overview and Symptoms
Users may experience critical session recall anomalies when operating UJAM plugins within Reason Studios environments.
- Observed Behavior: Saved .reason project files fail to load customized UJAM presets and parameter states.
- Specific Symptom: The plugin silently reverts to its hardcoded factory initialization state upon project load.
- Example: User saves a project using Virtual Bassist MELLOW with preset "Real Book" (internal phrase set "Four Beat Swing"). Upon reload, MELLOW ignores the saved matrix and loads the default state.
- Verified Environments: Documented explicitly in Reason 12.7.4d3 on Windows 10, but applicable across Reason 12 and Reason 13 architectures.
Technical Root Cause Analysis
Diagnostic telemetry confirms this is a host-side VST Parameter Mapping Cache Corruption, not an Audio Processor Value Tree State (APVTS) misattribution or serialization bug within the UJAM binary.
- Reason Studios compiles a localized metadata database (__PluginDatabase.dat) mapping VST parameter IDs to its Plugin Rack Device wrapper.
- If this database desynchronizes, Reason transmits session data targeting incorrect parameter indices during a session recall.
- The DAW triggers unexpected restartComponent(kParamTitlesChanged) events during load.
- To prevent a hard host crash, the UJAM binary aborts the corrupted data injection and defaults to its factory initialization.
Resolution: The Cold Boot Scan Protocol
To remediate this desynchronization, you must force Reason to execute a "Cold Boot" scan by deleting its parameter mapping cache files.
Step 1: Terminate the Host Process
Completely close the Reason application. Failing to do so will result in the OS enforcing a "File in Use" lock, or Reason writing the corrupted RAM data back to the drive upon exit.
Step 2: Delete Target Database Cache Files
Locate and delete the explicit database files according to your OS. Note: Delete any file prefixed with _PluginDatabase or PluginCache.
macOS Paths (Navigate via Finder -> Go -> Hold Option ⌥ -> Library):
~/Library/Application Support/Propellerhead Software/Reason/Caches
- _PluginDatabase.dat
- _PluginDatabase_v2.dat
- __PluginDatabase_v3.dat (and -arm64.dat variants)
- __PluginDatabase_v4.dat (and -arm64.dat variants)
- _PluginCache.dat
Windows Paths (Navigate via Run Dialog: Win + R -> %LocalAppData%):
C:\Users\<Your_Name>\AppData\Local\Propellerhead Software\Reason
- _PluginDatabase.dat
- _PluginDatabase_v2.dat
- __PluginDatabase_v3.dat
- __PluginDatabase_v4.dat
- PluginCache.dat
Step 3: Initialize Cold Boot
Launch Reason. The DAW will trigger a deep, bit-level interrogation of your VST directories to rebuild the cache from the UJAM binaries. Let this extended load sequence finish, then open your .reason project file.
Advanced Routing: Symbolic Links (Symlinks)
Do not attempt to manually troubleshoot or rewrite registry paths if Reason fails to scan plugins routed via symbolic links. Incorrect symlink configurations will continuously break the cache rebuilding process.
For all custom VST directory routing using symlinks, you must follow the exact protocol outlined in our dedicated documentation.
👉Windows Users: Managing Large .blob Files Using Symbolic Links on Windows
👉macOS Users: Managing Large .blob Files Using Symbolic Links on macOS
Reference & External Technical Documentation
For full technical context, external bug tracking, and related diagnostic behavior mapping across different architectural environments, refer to the following required reading:
DAW & APVTS Parameter Mapping Frameworks:
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